The prevalence of multiple hair whorls in a group of mentally retarded patients was 8% as opposed to 3.6% in a group of healthy children. A statistically significant relationship was demonstrated between mental retardation, multiple hair whorls, more than two dysmorphic features, and unusual dermatoglyphics. The results confirm the importance of multiple hair whorls as a genuine dysmorphic feature. The significance of these markers in the evaluation of mentally retarded subjects is discussed, with special reference to the timing of the fetal insult.