Estimates of the incidence of the Meckel syndrome (MS) from different parts of the world vary from 1:140,000 to 1:13,250 births. In this nationwide study performed in Finland, the incidence of 1:14,400 births was found by retrospective ascertainment during the period 1970-1979, while the incidence was 1:8,500 births when prospective monitoring was performed in 1980-1981. The most probable incidence in Finland is about 1:9,000 births. Autosomal recessive inheritance of MS is confirmed in this study. The ratio of affected sibs, corrected for truncate complete ascertainment, was 0.261. No consanguinity between parents was found, as marriages between close relatives are rare in Finland and the ancestors were not traced back far enough to find remote consanguinities.