Thirteen male newborns of a family spanning five generations revealed a syndrome consisting in elevated birth weight and length, a disproportionately large head with coarse, distinctive facies, short neck, slight obesity, and broad, short hands and feet. The affected who reached adulthood attained heights of about 2 m; their unusual facial and general appearance and the clumsiness of all their motions, remarkable during infancy and childhood, had become somewhat less conspicuous. In all but one affected individual, intellectual development was normal. In two index cases neither clinical nor laboratory evaluations revealed a basic defect. X-linked recessive inheritance is most probable.