Smith-Lemli-Opitz syndrome (SLO) is a autosomal recessively inherited disorder caused by an inborn error of cholesterol metabolism that results in deficiency of cholesterol and accumulation of the cholesterol precursor, 7-dehydrocholesterol. Two forms have been recognized based on clinical course and severity: the classical SLO (type I) and the lethal acrodysgenital syndrome (type II). Affected patients present with multiple congenital anomalies, growth restriction, and mental retardation. A 32 days old boy with the complaints of feeding difficulty, vomiting, and cyanosis diagnosed as Smith-Lemli-Opitz syndrome type I is presented. The measurement of serum cholesterol levels are important in the cases with ambiguous genitalia for exclusion of SLO.