Congenital sinuses on the lower lip in association with cleft lip, cleft palate, or both are rare and occur in four syndromes, namely Van der Woude syndrome, popliteal pterygium syndrome, orofacial digital syndrome, and the ankyloblepharon filiform adnatum. The most common and best studied among these--the Van der Woude syndrome--is believed to be due to an autosomally dominant gene with 80 to 100% penetrance and a variable expressivity. We present our study of 9 patients with congenital lower lip sinuses and the penetrance in their families. On the basis of our observations we conclude that this syndrome may have low penetrance among the populations studied.