Sclerosteosis is a unique autosomal recessive condition in which skeletal overgrowth is associated with syndactyly and digital malformation. Analysis of the course and clinical features in 25 affected individuals showed that the condition is progressive and potentially lethal. Facial palsy and deafness are common complications and raised intracranial pressure may develop. The clinical and radiographic stigmata of sclerosteosis permit differentiation from the other disorders of the "osteopetrosis" or "Albers-Schönberg disease" group, in which bony thickening and cranial nerve palsy occur.