Between 1983 and 1997 a total of 2029 children with CL/P (cleft lip, cleft lip and palate or cleft palate), who were born in the Bohemian districts of the Czech Republic and who underwent surgery and treatment at the Clinic of Plastic Surgery in Prague, were analysed. One possibility for decreasing the risk of delivery of a child with CL/P is to decrease or eliminate its prenatal exposure to embryotoxic factors. Detection of the embryotoxic factors acting at the individual level (e.g. elevated temperature, drug consumption, x-ray examination or infection) is easier than the detection of embryotoxic factors operating at the population level (e.g. water contamination, air pollution). When searching for the latter factors, we first have to reveal regional differences in CL/P incidence. The aim of the present paper was to determine significant differences in the mean incidence of newborns with CL/P in Bohemian districts during a 15 year period. The correlation between the incidence of CL/P and the birth rate in the different districts was also examined. The mean incidence of CL/P in all Bohemian districts was 1.86 per 1000 newborns (1.86/1000). Districts were di- vided into three groups, according to significant differences in the incidence of CL/P using a confidence interval. The lowest mean incidence of CL/P was detected in the Svitavy district (0.72/1000) and Louny (1.05/1000). The highest mean incidence was found in the Beroun district (2.86/1000). Besides Beroun, a high mean incidence of CL/P (more than 1.96/1000) was also found in Klatovy, Mělník, Tábor, Kolín, Semily, Česká Lípa, Pardubice, Teplice, Český Krumlov, Sokolov, Chomutov, Praha-západ, Jičín, Rakovník, Kladno, Prachatice, Rokycany, Tachov, Liberec , Pelhřimov. Paradoxically, the districts with a higher or lower birth rate exhibited a lower (1.62/1000) or higher (1.92/1000) incidence of CL/P, respectively. Future studies should elucidate whether the significant regional differences in the incidence of CL/P can be related to differing exposure of pregnant women to harmful environmental embryotoxic factors.

        Key words: orofacial cleft, cleft lip, cleft palate, epidemiology, human