The experience of the Preconceptional Clinic developed in our hospital from 1992 to 1996 is here reported. Twenty-eight insulin-dependent diabetic patients underwent a preconceptional control (PCC). Pregnancy was obtained in 19 patients (2 miscarriages, 12 full pregnancies, and 5 pregnancies in course). A comparative case-control study was performed between the 12 patients undergoing PCC, who have completed their pregnancy, and other 12 prepregnant diabetic patients, controlled from the 7-12 weeks of pregnancy. HbA1c levels in the PCC group were lower, and no differences regarding fetal morbidity were observed. The presence of a severe congenital malformation in the PCC group, with normal periconceptional HbA1c levels, denotes the teratogenic influence of factors yet to be elucidated.