SAMBAVA, Madagascar: Fifty kilometers outside this down-at-the-heels seaside town, Justin Betombo tends his vanilla plants and cheers the local soccer team as if he had not a care in the world. And in fact, what was once his greatest worry has been almost magically lifted from his shoulders.

In the prosecutor's office, a file filled with accusations that he had sodomized his 9-year-old niece has vanished.

Betombo was arrested in 2003 after the girl, Kenia, said he had savagely assaulted her. The police obtained his confession, which he later recanted, and a doctor's certificate that Kenia had been sexually violated, rendering her incontinent and anorexic. Twice they sent the case file to the local prosecutor.

There matters ended. Betombo attended one hearing in the prosecutor's office, of which Kenia's parents, who have been so frustrated by the handling of the case that they wanted her name and photograph to be published, said they knew nothing. The records are nowhere to be found. Betombo walked away a free man.

Among sub-Saharan Africa's children, this is a distressingly common story. Even as this region races to adopt many of the developed world's norms for children, from universal education to limits on child labor, child sexual abuse remains stubbornly difficult to eradicate.

In much of the continent, child advocates say, perpetrators are shielded by the traditionally low status of girls, a view that sexual abuse should be dealt with privately and justice systems that constitute obstacle courses for victims.

Data are sparse and sexual violence is notoriously underreported. But South African police reports give an inkling of the sweep of child victimization.

In the 12 months that ended in March 2005, the police estimated that there were about 23,000 cases of child rape. In contrast, England and Wales, with nine million more people than South Africa, reported 13,300 rapes of all females in the most recent 12-month period.

The problem is by no means unique to Africa. While a survey of nine countries last year by the World Health Organization found the highest incidence of child sexual abuse in Namibia - more than one in five women there reported having been sexually abused before the age of 15 - it also found high rates in Peru, Japan and Brazil, among others.

Relatives are frequent perpetrators, as in much of the rest of the world. But African children face added risks, especially at school: Half of Malawian schoolgirls surveyed in 2006 said teachers or classmates had touched them in a sexual manner without their permission. Abuse cases are on the rise in South Africa, Zimbabwe, Zambia, Uganda, Kenya and other African countries, statistics show. Whether that means more children are being victimized or more are coming forward, or both, is impossible to determine, experts said.

Researchers cite various reasons why abuse is so common: poverty, which makes it harder for parents to keep children safe; a legacy of violent, oppressed societies; and cultural mores that allow offenders to escape criminal punishment, often by marrying their victims or compensating their families.

But, ultimately, said Rachel Jewkes, an expert on sexual violence with South Africa's Medical Research Council, the vast gap between the status of men and boys on one hand and women and girls on the other explains much of the climate of relative tolerance.

Increasingly, African nations are openly acknowledging the problem, partly because AIDS has made children more likely to fall ill or die from abuse. Campaigns against child sexual abuse are under way in Zimbabwe, Lesotho, Swaziland, Sierra Leone and elsewhere.

South Africa is perhaps furthest along in developing the specialized courts, medical treatment and counseling that have long been standard in the West. But even there, Jewkes said, appalling police work, like failure to verify the addresses of perpetrators and victims, routinely dooms prosecutions.

Beyond that, said Joan van Niekerk, head of Childline, which runs the nation's child-crisis hot lines, children regularly complain that coping with the criminal justice system is worse than the sexual abuse itself.

Kenia's father and mother are passionate about the need for justice for their daughter Kenia. But after four fruitless years, they said, they have all but given up hope.

One night in mid-2002, Kenia said, her uncle summoned her to his bed. "Because I refused, he came over to my bed," she said. Afterward, she said, he told her: "If you talk about what happened I will kill you."

Months later, Kenia, whose bowel had been severely damaged, told a neighbor. Nearly four years of medical procedures, including a colostomy, followed.

Kenia's parents were forced to sell their rice field and move to the northern city of Diego for Kenia's treatment. Kenia, now 13, is temporarily in Antananarivo, where a doctor is trying to treat her with a specialized diet.

A surgeon who examined her this month said a full recovery was unlikely. The uncertainty preys on Kenia, her mother said. "Sometimes she tells me, 'My body is hurting. I have so many problems. I don't go to school. I just feel this sickness all around me,'" she said.

Betombo and his wife both denied Kenia's account. But ultimately - after the police beat him, Betombo said - he signed a confession and was arrested.

Betombo said he had persuaded the prosecutor that his confession was false. Kenia's parents said they were never summoned to contradict him.

"I took this girl in as my daughter. I really can't understand why they say that I could have done such an awful thing to her," Betombo said.

Sambava's police sent the file to the prosecutor's office again a few months later. But Sophie Ramahakaraha, the prosecutor in charge, said she that had no record or memory of it. Real instances of child rape, she said, are rare. "Very often the parents are poor," she said, "and they use this procedure to get money."

But to Daul Randriamalaza, a Sambava police inspector, there is no question about who was the victim here.

"I don't want to talk about corruption here, but that is what could have happened in this case," he said.

"I have children myself. How can I be happy about this?"