Long bone involvement is almost universal in ECD patients and is bilateral and symmetrical in nature. More than 50% of cases have some sort of extraskeletal involvement. This can include kidney, skin, brain and lung involvement, and less frequently retroorbital tissue, pituitary gland and heart involvement is observed. Bone pain is the most frequent of all symptoms associated with ECD and mainly affects the lower limbs, knees and ankles. The pain is often described as mild but permanent, and juxtaarticular in nature. Exophthalmos occurs in some patients and is usually bilateral, symmetric and painless. In most cases it occurs several years before the final diagnosis.