The authors describe the case of a family in which two siblings affected by cleft palate and cheiloschisis were diagnosed as suffering from van der Woude's syndrome (VWS). The diagnosis was largely determined by the finding of mucous cysts (lip-pits) on the lower lip of the two patients and their mother. Classification as VWS enabled genetic counseling as to the risk of recurrence to be modified from multifactorial to autosomal dominant. The authors also consider aspects of differential diagnosis among van der Woude syndrome, pterygo -popliteal syndrome and labio or palatoschisis syndrome with filiform fusion of the eyelids.