Progressive diaphyseal dysplasia (Camurati-Engelmann disease) is a rare hereditary disorder of bone characterized by progressive, bilaterally symmetrical diaphyseal sclerosis of the long bones. Severely affected patients show muscle weakness, waddling gait and severe pain in the extremities. However, clinical and radiological investigations in families with Camurati-Engelmann disease demonstrate a wide variability in expression of the manifestations. Asymptomatic patients were in several instances diagnosed only after radiologic screening of relatives. Although considered an autosomal dominant disorder, families are described where neither clinical nor radiological manifestations can be demonstrated in direct ancestors of patients. Combining roentgenographic examination with bone scintigraphy seems therefore necessary in confirming or ruling out progressive diaphyseal dysplasia in each family member.