We describe two male patients with a 46,XY,-18,+der(18),t(7;18) (q31.2;q23)mat karyotype. Previously, 22 other patients with dup(7q) have been described, but only four of them had duplication of segment 7q31----7qter. The two patients in this study were ascertained independently and lived in different states. However, because of the rarity of this translocation, the patients were suspected to be related. The families were investigated extensively, and the patients were found to be third cousins once removed. Both patients had severe hypospadias, large fontanelles, cleft palate, and minor facial anomalies (square and prominent forehead, short, downslanting palpebral fissures, long eyelashes, long philtrum, short nose, thin vermilion border with downcurved upper lip). Their phenotypes were compared with those of previously described patients. One of the two patients described here is alive at 23 months and is the oldest known living patient with this chromosome abnormality. Apneic spells often are present and may be secondary to severe brain abnormalities, such as those identified in our two patients.