Echocardiographic studies were performed in 42 sets of parents who had at least one infant with Sudden Infant Death Syndrome (SIDS). Asymmetric septal hypertrophy (ASH) was detected by echocardiography in one member of only 5 percent of the 42 sets of parents. Echocardiograms were also obtained in three other sets of parents who had infants with SIDS (selected because their infants showed small foci of disorganized cardiac muscle cells in the ventricular septum, similar to those present in patients with typical ASH but less marked in severity). ASH was present in one member of each of these three sets of parents. Ventricular septal‐to‐posterobasal left ventricular wall thickness ratios in the five subjects in this study with echocardiographically determined ASH ranged from 1.3 to 1.7, although only one individual showed marked thickening of the ventricular septum (22 mm). Thus, SIDS and ASH do not appear to be commonly associated conditions.