We describe a boy with the syndrome due to dup(17q) resulting from a paternal balanced t(12;17) (q24;q23). The comparison of the clinical findings in our patient with those previously reported shows that the dup(17q23----qter) is associated with a clinically recognizable syndrome. Anomalies present in greater than or equal to 75% of the patients were severe psychomotor retardation; short stature; microcephaly; frontal bossing and temporal retraction; widow's peak; narrow palpebral fissures; flat nasal bridge; thin upper lip overlapping thin lower lip; downturned corners of the mouth; apparently low-set, posteriorly angulated and malformed ears; low posterior hairline; widely spaced nipples; cryptorchidism; proximal limb shortness; and hyperlaxity of limb joints. The translocation carrier father of our patient had a Poland anomaly.