We aimed to assess the impact of a preconceptional clinic (PC) on the perinatal outcome (PO) of diabetic pregnancies attended in our centre. We studied 185 pregnancies attended in the 1986-1996 period (152 in women with insulin dependent diabetes mellitus (IDDM) and 33 with non insulin-dependent diabetes mellitus (NIDDM)) and we analysed the perinatal outcome for both mother and fetus. Sixty-six women (36.1%) had enrolled in the PC, 41.4% for IDDM and 9.1% for NIDDM pregnancies, p < 0.01. First pregnancy HbA1c (in SD around the mean) was 3.98 +/- 3.00 in non-attenders (NA) vs 2.57 +/- 2.41 in attenders (A), p < 0.01. The final HbA1c was in the normal range in both groups. D-R class according to White classification was 33.0% for NA vs 54.5% for A, p < 0.01. There were no differences in the rates of abortion and major malformations (8.8% NA vs 3.6% A, ns). Both groups differed in the rate of cesarean sections (54.9% NA vs 71.0% A, p < 0.05) and in the rate of small for gestational age infants (SGA) (8.7% NA vs 1.8% A, p < 0.05). There were no differences between groups in maternal or neonatal outcomes. In this group of diabetic women with a moderate although less than optimal metabolic control at the beginning of pregnancy, the impact of PC on PO is less evident than described.