AbstractFrom 1983 through 1987, in a California population of 718,208 births, 237 infants were born with a congenital diaphragmatic hernia (CDH), a birth prevalence of 3.30 per 10,000 total births (live births and stillbirths). We proposed that the various types of this defect, characterized by their different pathogeneses, would be reflected in differences in their descriptive epidemiologies. We evaluated various demographic, maternal, and infant characteristics for three major types of defects, the Morgagni hernia, the pars sternalis hernia, and the posterolateral hernia, categorizing the latter type into isolated defect (N = 129), multiple congenital anomalies including nonchromosomal syndromes (N = 86), trisomies (N = 10), and chromosomal anomalies other than trisomies (N = 2). For the posterolateral hernia, we present the distribution of associated anomalies (43%) and specifically of midline defects (19%). Although the number of cases for the Morgagni hernia (N = 5) and the pars sternalis hernia (N = 5) were small, comparisons with the posterolateral hernia suggested lower sex ratios, of borderline significance for the pars sternalis hernia (P<0.09), and higher mean maternal ages for both groups. Within the posterolateral type, we found a significantly higher male to female ratio (M/F = 1.58) only for the isolated subgroup compared to the population (P<0.03), and a borderline significant rural/urban difference in prevalences (2.12 vs. 1.45 per 10,000) (P<0.06). Additionally, the distribution of monthly prevalence rates adjusted for gestational age suggested opposite seasonal trends between the isolated and the other posterolateral hernias; within this latter subgroup the difference between the highest monthly rate (1.68) and the lowest (0.96) was of borderline significance (P<0.09). Our results suggest the need to consider the respective types and subgroups of CDH separately in epidemiologic studies. © 1992 Wiley‐Liss, I