A trisomy for the distal short arm of chromosome 2 (2p23 leads to 2pter) resulted in similar phenotypic and developmental abnormalities in three related males. The cytogenetic defect was traced to a familial balanced 2;3 translocation [t(2;3) (p23;27)]. Comparison of these patients with the seven previously published cases of 2p partial trisomy reveals a pattern of common features including severe mental and growth retardation, a characteristics facial dysmorphism particularly affecting the eyes, abnormalities of the sternum, spine, and digits, a heart defect, and, in males, cryptorchidism and a striking genital anomaly consisting of a very small penis buried in dorsally fused scrotal skin.