We describe a patient with adult-type osteopetrosis presenting as carpal tunnel syndrome. Radiographs demonstrated sclerosis of the carpal bones, bone biopsy revealed wide bone spicules containing areas of cartilage, and electrophysiologic studies confirmed the diagnasis of median nerve entrapment in the carpal tunnel. Any condition which alters the size or shape of the carpal canal or its contents may result in median nerve compression.Osteopetrosis is a rare bone disease, caused by disequilibrium between the normally balanced process of bone formation and bone resorption (1). In this report, we present a case of adult-type osteopetrosis in which the patient presented with carpal tunnel syndrome. The clinical, radiologic, and histologic features of the disease, including the electrodiagnostic findings, are discussed.Case report. A 52-year-old woman was admitted to the hospital because of numbness and a tingling sensation in her left hand. The sensation was more pronounced at night. Seven years prior to admission she had renal colic, and subsequently a calculus was removed from her right kidney. A skeletal survey at that time revealed a diffuse increase in bone density.Dysesthesia in the median nerve distribution of the left hand was noted at her physical examination. Tinel's sign, blood pressure cuff test, and Fhalen's wrist-flexion test results were positive. Laboratory findings, including levels of parathyroid hormone, hydroxyproline, alkaline phosphatase, and a thyroid profile were all within normal range. The patient was advised to undergo surgical release of the carpal tunnel, she refused, and the condition persisted.A posteroanterior view of the wrist, a radiograph of the spine, and the results of a bone biopsy are shown in Figures 1, 2, and 3, respectively.Results of electrodiagnostic tests (Figure 4) were as follows: reduced amplitude of sensory-evoked potentials of the median nerve, marked prolongation of the distal sensory latency (6.0 ms; normal <3.7), and increased motor distal latency of the median nerve (4.9 ms; normal c4.3). Nerve conduction velocities of the median nerve were normal (50 metershecond) (2).Discussion. Osteopetrosis, also known as Albers-Schonberg disease or marble bones disease, is a rare osseous disorder. Its etiology is not completely understood (3).The disease is characterized by a general increase in bone mass. Current opinion is that osteopetrosis is a disease of the osteoclast. Numerous osteoclasts may be present, but do not appear to be engaged in the resorption of bone. Two forms are recognized. The severe form is inherited as an autosomal recessive trait (4).