Objective: to perform comparative analyses of obstetric and perinatal outcomes between type 1 diabetic pregnancies (T1DM) and the general obstetric population in Sweden between 1991 and 2003. Research design and Methods: Population based study. Data were obtained from the Medical Birth Registry, covering more than 98% of all pregnancies in Sweden. A total of 5,089 T1DM pregnancies and 1,260,207 controls were included. Odds ratios (OR) were adjusted for group differences in maternal age, parity, BMI, chronic hypertensive disease, smoking habits and ethnicity. Results: In T1DM, preeclampsia was significantly more frequent [OR=4.47 (3.77-5.31)] as well as delivery with Cesarean section [OR=5.31 (4.97-5.69)] compared to the general population. Stillbirth [OR=3.34 (2.46-4.55)], perinatal mortality [OR=3.29 (2.50-4.33)] and major malformations [OR=2.50 (2.13-2.94)] were more common in T1DM than in controls. Risk of very preterm birth (