Older, powerful men boosted their social status by keeping boys as sexual playthings and the practice was celebrated in song and dance, a military study claimed.
British officers in Helmand requested the study to help them understand the sexual behaviour of locals and Afghan comrades after young soldiers became uneasy they were being propositioned.
American social scientists employed to help troops understand the local culture reported that homosexual sex was widespread among the Pashtun ethnic group in southern Afghanistan.
Strict separation of men and women, coupled with poverty and the significant expense of getting married, contributed to young men turning to each other for sexual companionship.
"To dismiss the existence of this dynamic out of desire to avoid western discomfort is to risk failing to comprehend an essential social force underlying Pashtun culture," the report said.
The study, called 'Pashtun Sexuality', said that as well as willing sex between young men, "boys are appreciated for physical beauty and apprenticed to older men for their sexual initiation".
The practice of 'bache bazi' or boy play, is known throughout Afghanistan, but is particularly renowned in the city of Kandahar next to Helmand, where prepubescent boys are widely admired.
Western soldiers often report feeling unease at the attentions of their Afghan comrades, who are affectionate with each other and sometimes wear make-up.
British troops have also talked of their disgust at police or militias keeping young boys as hangers on.
Anna Maria Cardinalli, author of the report, said British officers requested the research in the summer of 2009 when she worked with them in Lashkar Gah.
She said: "They were having young men who were beginning to feel uncomfortable because they felt they were being approached." She said the study gave no advice about what action troops should take if they confronted paedophilia.
A spokesman for the Ministry of Defence said: “Afghanistan is a sovereign nation with its own law under which the sexual abuse of children is illegal.
“British forces working as part the wider [coalition] force continue to work with and assist the Afghan National Security Forces, including the Afghan National Army and Afghan Police, to ensure that the rule of law in Afghanistan is adhered to and upheld.”