A 6-month-old Japanese boy with trisomy 17p, resulting from a paternal balanced translocation t(5;17)(p15;p11), is described. Comparison of his clinical features with those of two previously reported patients with trisomy 17p revealed a characteristic combination of clinical features. They included intra- and extra-uterine growth retardation, developmental retardation, microcephaly, internal hydrocephalus, a facies with lateral displacement of the inner canthi, antimongoloid slanting of the palpebral fissures, a broad nasal bridge, and micrognathism, low-set, large and simple ears, a short and webbed neck, and flexion deformities of the fingers. The external genitalia in the two male patients were characterized by a small penis, undescended testes and a hypoplastic scrotum. Congenital cardiac defect was present in two of the three patients.