Two pairs of siblings are described with proportionate dwarfism due to skeletal hypoplasia of prenatal onset. The head size was normal for age and disproportionately large for height. The patients had a characteristic face different from that seen in the Silver-Russell syndrome. The family data are in accordance with autosomal recessive inheritance. In spite of some similarities, the bulk of clinical and genetic evidence suggests that the described intrauterine growth retardation syndrome is different from the Silver-Russell syndrome and presents an apparently "new" entity which has been designated 3-M syndrome.