To estimate the risk of structural birth defects (i.e. congenital abnormalities [CA]) in the offspring of pregnant women with type 1 (DM-1), type 2 (DM-2) and gestational diabetes mellitus (GDM) and to check the efficacy of recent specific care of diabetic pregnant women in the reduction of DM-related CA. Comparison was made of the occurrence of medically recorded types of diabetes mellitus in pregnant women who had malformed fetuses/newborns (cases) and who delivered healthy babies (controls) in the population-based Hungarian Case-Control Surveillance System of Congenital Abnormalities, 1980-1996. In the case group, which included 22 843 offspring, there were 79 (0.35%) pregnant women with DM-1, 77 (0.34%) pregnant women with DM-2 and 120 (0.53%) pregnant women with GDM. The control group comprised 38 151 newborns, and 88 (0.23%), 141 (0.37%) and 229 (0.60%) pregnant women with DM-1, DM-2 and GDM, respectively. The total rate of cases with CA was higher only in the DM-1 group (adjusted OR with 95% CI: 1.5, 1.1-2.0) and within four specific types/groups: isolated renal a/dysgenesis, obstructive CA of the urinary tract, cardiovascular CA and multiple CA; namely, caudal dysplasia sequence. The risk of total CA was lower in the present study compared to the risk in previous studies and the DM-1-related spectrum of CA was also different. There was no higher risk of total CA in the offspring of pregnant women with DM-2 and GDM. The certain part of maternal teratogenic effect of DM-1 is preventable with appropriate periconceptional and prenatal care of diabetic women.