This was a follow-up study of earlier reported findings by the present investigators suggesting, albeit equivocally, that separation during early childhood inhibited later sexual acts of a potentially procreative nature between siblings but did not deter other sexual activity. The present study surveyed 170 subjects, mostly in the Toronto area, by telephone and mail. Respondents reporting potentially procreative, postchildhood sexual acts (attempted or completed genital intercourse) with siblings were compared with those reporting sexual relationships excluding procreative acts, and a third sample reporting no postchildhood sibling sexual behavior. Consonant with expectations from the earlier study, prolonged separation during early childhood was associated with procreative postchildhood sexual activity but not with other postchildhood sexual activity. Contrary to predictions, however, both sexual activity groups reported significantly more nudity and physical contact with siblings during childhood than subjects reporting no sexual activity. The findings are discussed in terms of a revised version of the Westermarck hypothesis, which is consistent with a domain-specific approach to evolved incest avoidance mechanisms.