A genetic and epidemiological analysis was carried out on 1, 574 patients with cleft lip and/or cleft palate (CL/CP) who visited the clinic of Second Department of Oral and Maxillo-facial Surgery, Tokyo Medical and Dental University Hospital from 1960 to 1987. These patients are evaluated with respect to sex ratio, laterality, and family study. The family study includes the rate of affected families, the relationship of the type of cleft between the probands and their parents and siblings, the affected rates of the parents and siblings, the culculation of affected rates of parents and siblings of the probands in polygenic inheritance by Edwards, and the culculation of Penrose's expected relative frequency of siblings of the probands. The results of analysis above indicated that CL/CP is most likely to have the character of multifactorial inheritance.