From July 1, 1985 to June 31, 1987, the birth defect monitoring was carried out in 30 hospitals in Anhui Province. It was found that there were 116 cases of cleft lip (CL) and cleft palate (CP) in 46,811 perinatals. The incidence rate of CL and/or CP was 2.48%. It was higher level both in China and abroad. Among these cases, there were 105 cases (90.52%) with CL +/- CP. The incidence rate of CL and CP related to maternal age, birth order, educated level, resident place, occupation and pregnant season was studied. The frequency of first degree relative was 28.26%. That was about thirteen times higher than the birth population frequency. The incidence rate in the offspring of parental-consanguinity was 9.53% (9/944). This is significantly higher than that of non-consanguineous marriage (P less than 0.001). There were three same sex twins affected by CL +/- CP in the 548 pairs of twins, none of the twins with CL +/- CP had identical one. Only one pair of the female twins was affected by different defects. The heritability was found to be 59.6% and was lower than data in other reports. It suggests that environmental factors play a major role in the etiology.