We report on a sclerosing bone dysplasia, associated with cutis laxa, enamel dysplasia, and mental retardation. The patient was a 17-year-old Japanese boy of normal height and muscular build. Cutis laxa with prominent veins in the scalp and abdominal wall and delayed eruption of permanent teeth attracted the attention of clinicians in infancy and adolescence, respectively. The clinical manifestations included a progeroid facial appearance with prognathism, wrinkled skin, and interdigital webbing. The intelligence quotient was estimated at 60. Enamel dysplasia was histologically confirmed. Skeletal changes included calvarial hyperostosis, sclerosis of the skull base, an enlarged, sclerotic mandible, broad clavicles and ribs, and diaphyseal undermodeling of the tubular bones. Metaepiphyseal sclerosis or longitudinal striation was found in the long bones. Metaphyseal equivalents of the axial skeleton showed dense osteosclerosis. These clinical and radiological manifestations overlapped with those of Lenz-Majewski syndrome. Unlike the classical phenotype of the disorder, however, he did not show brachymesophalangy with proximal symphalangism or growth failure. The present case may be considered to fall in the mildest end in the phenotypic continuum of Lenz-Majewski syndrome, suggesting that the clinical spectrum of the disorder may be broader than currently thought.