Congenital posterolateral diaphragmatic hernia (CDH) is widely regarded as an isolated defect, but this view is incomplete. We reviewed our clinical and autopsy experience and the literature from the past 25 years in order to catalogue the frequency and clinical importance of additional malformations in patients with CDH. The study showed two broad categories of patients. In the larger group of infants (65 of 108, or 60%), CDH was the only severe defect, apart from those normally associated with the presence of abdominal viscera in the thorax. Thirty-six of these patients (55%) survived. A striking finding among infants with isolated CDH, not previously highlighted in the literature, was cryptorchidism which was present in 30% of males. By contrast, 43 patients (40%) had one or more severe extradiaphragmatic malformations; only six of these infants (14%) survived. Defects in morphogenesis were widespread, heterogeneous, and seemingly related to numerous pathogenetic mechanisms. Most often abnormalities involved the heart, brain, genitourinary system, craniofacial region, or limbs. The high incidence of multiple anomalies in some patients with CDH should influence our investigations into causes and mechanisms. Patients with CDH should be evaluated carefully for additional defects--their presence has a significant impact on management and worsens prognosis.