A retrospective epidemiological study of cleft lip and palate in King County, Washington, between 1956 and 1965 is reported. Multiple sources of ascertainment were employed, and particular attention was given to obtaining information concerning other associated malformations. Occurrences of cleft lip (CL), cleft lip and palate (CL + P), and cleft palate (CP) were analyzed by separate categories, depending on the presence or absence of associated major or minor malformations. The results strongly indicated that clefts with associated malformations are different epidemiological entities from pure clefts. Sex-ratio reversals occurred for some categories with associated malformations. In contrast to the usual male excess of CL f P, there was a female excess of CL f P with major associated malformations. In contrast to the usual female excess of CP, 49% of children with CP with associated malformations were male. No maternal-age effect was observed for any "pure" cleft category, but significant "U-shaped maternal-age distributions were seen for CL + P with associated major malformations, CP with associated major malformations, and CP with all associated malformations. Increased frequency of low birth weight and infant mortality were confined to categories with associated malformations. No significant birth order, season, secular change, or time-space clustering effects were observed. The incidence rate for all clefts was 1.84/1000 live births.