The aim of this study was to investigate the one-year developmental outcome of offspring of mothers with pregestational diabetes mellitus (PGDM). We prospectively evaluated 31 women with PGDM (21 with type 1 DM and 10 with type 2 DM) and 41 nondiabetic controls during pregnancy and for one year follow-up. Data showed that offspring of mothers with PGDM scored lower than controls in all aspects of development--mental, psychomotor, and exploration/orientation. Despite the good metabolic control of the mothers with PGDM, their offpsring showed a less favorable developmental outcome at one year than infants of nondiabetic mothers. MDI score and PDI score were significantly lower in the diabetic group than in the controls (91.04 vs 98.15, p<0.05 and 85.15 vs 95.54, p<0.05, respectively). In addition, the orientation/engagement score was lower in the diabetic group as compared with the nondiabetic group (41.04 vs 45.50, p<0.05). Whereas no significant difference was found between the type 1 and type 2 groups with regard to the MDI score, type 2 infants scored lower on the PDI than infants in the type 1 group (78.1 vs 89.3) but higher on the motor quality score (34.0 vs 31.3). These preliminary findings support the need for ongoing large scale developmental follow-up studies of offspring born to diabetic mothers in order to elucidate whether they have cognitive impairment later in life.