We review six families in which recurrence of achondroplasia, inexplicable through autosomal dominant inheritance, has occurred. The clinical and radiographic characteristics of affected individuals in these families are identical to those usually seen in achondroplasia. Family histories and parental characteristics likewise seemed not to set this group apart from others with achondroplasia. While various mechanisms for these occurrences of achondroplasia in family members related through unaffected relatives can be postulated, the hypothesis that these recurrences were simply the result of two independent chance events cannot, at least for the moment, be excluded.