The objective of this paper is to determine the frequency and outcome of asymmetrical septal hypertrophy (ASH) in large-for-gestational-age infants (LGA) born to diabetic (DM) and nondiabetic mothers (NDM), and to establish the relationship between ASH and maternal diabetes control. A comparative study was design to assess ASH in infants born to DM and NDM. The study was conducted in the Departments of Neonatology and Pediatric Cardiology of the "Hospital de Gineco-Pediatria 48", Instituto Mexicano del Seguro Social from January to December 1997. Eighty-five full-term infants of DM (group A) and 85 LGA infants of NDM (group B) were included. As a control group (group C), we studied 85 healthy, full-term infants. In all cases a Doppler echocardiogram was obtained in the first 48 h after birth, and for the ASH infants, at 2 and 4 months. Chest X ray, electrocardiogram, and laboratory tests were performed as complementary studies. ASH was present in 38.8% of LGA infants of DM and in 7.1% of NDM. The difference was significant (p < 0.01). Interventricular septum (IVS) and IVS/ posterior wall of left ventricle ratio were significantly different between groups A and B with C. There was no correlation between Hb A1 level and the presence of ASH in group A. ASH is a common finding in infants of DM. We could not find a relationship between the degree of metabolic control during pregnancy and the incidence and severity of ASH.