Two half-brothers are described who had developmental delay and minor dysmorphic features, both of whom had operative treatment for pyloric stenosis. They had identical unbalanced karyotypes: 46,XY,-17,+der(17)t(8;17) (q24;q25). This was inherited from their mother who had the balanced form of the translocation. She was of normal intelligence and had no history of pyloric stenosis herself or in her extended family. It is suggested that the unbalanced chromosomal rearrangement could have been associated with the development of pyloric stenosis in these two brothers.