We describe the clinical effects of cholesterol supplementation in 6 children with the RSH-"Smith-Lemli-Opitz" syndrome (SLOS). The children ranged in age from birth to 11 years at the onset of therapy, with pretreatment cholesterol levels ranging from 8 to 62 mg/dl. Clinical benefits of therapy were seen in all patients, irrespective of age at onset of treatment, or severity of cholesterol defect. Effects of treatment included improved growth, more rapid developmental progress, and a lessening of problem behaviors. Pubertal progression in older patients, a better tolerance of infection, improvement of gastrointestinal symptoms, and a diminution in photosensitivity and skin rashes were also noted. There were no adverse reactions to treatment with cholesterol. This preliminary study suggests that cholesterol supplementation may be of benefit to patients with the SLOS.