Cushing's syndrome is rare in pregnancy but can cause spontaneous abortion, stillbirth or premature birth. We report a case of transient hypertrophic obstructive cardiomyopathy in a newborn whose mother had hypercortisolism due to a primary adrenal lesion. There was no family history of hypertrophic obstructive cardiomyopathy. Follow‐up revealed complete resolution of the cardiac abnormalities in the infant. Cushing's syndrome in the mother resolved after delivery. Although maternal hypercortisolism seldom results in symptomatic hypercortisolism in the newborn, hypertrophic obstructive cardiomyopathy can occur.