Abstract Objective: To determine if seasonal variation in the incidence of oral-facial clefts exists in the Hong Kong Chinese population. Methods: Cases of non-syndromal oral-facial clefts identified from the Prenatal Diagnostic Clinic database from 2002-2009, and total births from our departmental statistics during this period, were used to calculate the averaged month-of-conception incidence for overall cases and individual categories of clefts, including cleft lip (CL), cleft palate (CP), cleft lip with/without cleft palate (CL+/-CP), and cleft lip with cleft palate (CLP). Results: There were 59 eligible cases (1.21/1000 births), including 25 CL, 12 CP and 22 CLP cases. The peak incidence was in February (1.96/1000 births) and the lowest in September (0.67/1000 births). There was significant inverse correlation with the months from winter (December) to autumn (November) for all categories except for CP. When analysed by seasons, significant inverse correlation from winter to autumn was observed for all categories, and significant differences in incidence was demonstrated for CL+/-CP and CL. Conclusions: The seasonality in the incidence of oral-facial clefts found in this study suggested that environmental factors are probably involved, which would have accounted for the reported seasonal variations and geographical and racial differences in the incidence in the literature.