Background: The risk of congenital malformations is two to three times higher among women with diabetes mellitus before pregnancy. Gestacional diabetes is emerging as a risk factor for malformations. Aim: To study the rate and type of congenital malformations among offspring of women with pre-gestational or gestational diabetes. Material and methods: A search in the databases of the Collaborative Latin American Study for Congenital Malformations and of the Neonatology Unity of The University of Chile Clinical Hospital. All births from January 1998 through June 2004 were investigated. Results: In the study period, 13,965 births occurred, of which 0.7% were stillbirths and 8.1% had malformations. A total of 295 women (2.1%) had diabetes (gestational diabetes in 1.8% and pre gestational diabetes in 0.3%). The prevalence of congenital malformations was 14% and 18.3% among offspring of mothers with pre-gestational and gestational diabetes, respectively (p=NS). The prevalence of congenital malformations among offspring of non diabetic women was 7.9% (p <0.001 with respect to diabetic women). Major malformations were found in 83% and 70% of malformed offspring of women with pre-gestational and gestational diabetes, respectively. Conclusions: Pregnant women with pre-existing or gestational diabetes have a higher risk of giving birth a child with malformations