Inevitably, in a wide ranging review, there will be some important omissions. The main difficulties in assessing the available information have been the lack, in so many studies, of analysis along gender lines, the lack of control groups, and, in many instances, too small sample size. Despite these limitations there has, over the past decade, been an upsurge of interest in and awareness of the significance of the sexual abuse of boys. It permits us to identify a number of important trends and to draw certain conclusions. Firstly, the scale of the sexual abuse of boys is much greater than was believed 10 years ago. There is no reason to think this is simply an artifact of definition, or information gathering, or indeed of an increased willingness to recognize abusive behaviour between children, even though these will all have an effect. Whilst the trend is clear, the actual prevalence rate is difficult to determine, with a reported range of between 3% and 31%. A current 'best guess' suggests contact abuse in the range of 2-5% in the male population. As each study controls for its own definition of abuse, the narrowing in the ratio of boys to girls abused can be accepted as quite reliable, and additional evidence of a delayed recognition effect. Retrospective community evidence shows 1 boy is abused for every 2-4 girls abused. In contrast, the highest clinical ratios are for 1 boy to every 4 girls. Those who work with runaways, male child prostitutes, or child and adolescent psychiatric inpatient units appear particularly likely to encounter abused boys. Secondly, a variety of explanations have been advanced to explain the apparent under-reporting or under-detection of the sexual abuse of boys. Prominent among them have been the boy's fears of disbelief and of being labelled homosexual. Police patterns of reporting extra-familial abuse may mask its extent from protection or health agencies, which is important because extra-familial abuse does appear to be more common in boys, especially older boys, than girls. Although there has been some diminution of the cultural denial that girls can be abused, a parallel decrease of denial regarding boys has lagged behind. This is particularly true of father-son and of the much less common mother-son abuse. It is plausible that certain 'alertors' are more relevant for boys. The recent development of aggressive behaviour, homophobic anxiety, co-abuse of a sibling and abusing behaviour in particular deserve consideration.(ABSTRACT TRUNCATED AT 400 WORDS)