A diagnosis of Smith-Lemli-Opitz syndrome was made shortly after birth in a small-for-dates infant, on the basis of a characteristic face, penoscrotal hypospadias, bilateral postaxial hexadactyly, and bilateral syndactyly of toes 2-3. The clinical course was marked by failure to thrive, severe delay, refractory myoclonic jerks beginning at age 2 months, and increasing hepatosplenomegaly. He developed corneal clouding and increased gingival hypertrophy and died at age 18 weeks. Autopsy disclosed widespread storage of mucopolysaccharides and lipids within the macrophages and, to a lesser extent, parenchymal cells, of all organ systems. There was extensive demyelination of the cerebral white matter, and dystrophic calcification in the cerebrum, cerebellum, and brainstem. There was no evidence of primary neuronal involvement in the storage. Although the chance concurrence of 2 uncommon diseases is rare, a causal link between the clinical anomalies and the storage disorder cannot be argued convincingly on the basis of one case. Careful pathologic studies of other children who die with clinical signs compatible with Smith-Lemli-Opitz syndrome are indicated.