Tint et al. [N Engl J Med 1994, 330:107-113], working with blood samples from the Smith-Lemli-Opitz syndrome (SLOS) patients of Irons and Elias showed the biochemical basis of this disorder to be a cholesterol biosynthesis defect [Irons et al., Lancet, 1993, 341:1414]. Based on this finding, clinical protocols for cholesterol and bile acid replacement therapy were established in a few centers including the University of Pittsburgh. We report our experience with bile acid and/or cholesterol replacement therapy in six patients with SLOS, now aged 3-27 years, with a confirmed biochemical diagnosis. Levels of plasma cholesterol and 7-dehydrocholesterol were correlated with periodic clinical evaluations over 8-27 months of therapy. There was a marked improvement in the growth of all the children. There was also an increase in the plasma cholesterol level in all the children and an overall increase in their percent sterol as cholesterol. Subjective improvement was also noted in their development. Although there was no significant change in the plasma cholesterol level of the older patients, there was a marked improvement in their behavior and in their quality of life.