Nine hundred and eighty-eight cleft patients born between 1950 and 1983 were registered in the Cleft Palate Clinic file at the University Pediatric Hospital, Medical Sciences Campus, University of Puerto Rico. The entire cleft population was studied to establish relationships among place of birth, sex, age, type of cleft, severity of cleft involvement, and lip side preference and to determine prevalence. The distribution of registered cleft patients by geographic region in Puerto Rico was similar to the distribution of the total population. Cleft patients occurred most frequently in the Northeast regions which have the greatest population density in the Island. Among the 988 cleft patients who were studied, the sex ratio (males to females) was slightly higher than one (1.06). This ratio was found to be similar to the sex ratio for births in Puerto Rico. The sex ratio varied among the different types of clefts: unilateral cleft lip and palate had the highest male to female sex ratio (1.7) and cleft palate alone had the lowest (0.6). Unilateral clefts of the primary and secondary palates were more common than bilateral clefts by a two-to-one ratio. Left sided cleft was more common than right sided cleft in unilateral cleft of the primary palate alone or combined with cleft of the secondary palate. A significant increase in prevalence of the cleft defect per year was observed until 1971. For all types of clefts the increased rate per year was 2.10 per hundred thousand.