This paper reports sporadic occurrence of the Pfeiffer syndrome with Kleeblattschädel (KS) in a male infant who died at 6 months of pneumonia with signs of increased intracranial pressure and who was found to have hydrocephalus, polymicrogyria, cerebellar herniation, bicuspid aortic valve, a common mesentery, absence of lesser omentum, hypoplasia of gallbladder, a single umbilical artery, and multiple eye defects. This case is presumed to represent a new mutation: in other families the Pfeiffer syndrome has been dominantly inherited. The Pfeiffer syndrome is a form of acrocephalosyndactyly and impresses clinically as a mild form of the Apert syndrome. The Kleeblattschädel is an etiologically non-specific developmental field defect (DFC); about two fifths of 51 known cases have apparent thanatophoric dwarfism and about one fifth are probable or possible examples of the Pfeiffer syndrome. The KS-DFC has also been seen in the syndromes of Carpenter, Apert and Crouzon.