Osteomesopyknosis is a bone disorder characterized by abnormal hardening of bone (osteosclerosis). It is generally limited to the axial spine, pelvis, and proximal part of the long bones, which is what distinguishes this condition from other sclerosing bone disorders. It is usually diagnosed incidentally in young adults complaining of back pain. Osteomesopyknosis is inherited in an autosomal dominant manner but the genetic cause has not yet been identified. It is generally benign and life expectancy is normal.

There are cases of association with other findings such as ovarian sclerosis and lymphoma; however, it is uncertain whether they have been coincidental or features of the disorder.

There have been reported cases where both parents of an affected person did not appear to have the condition. The chance of having signs and symptoms when the responsible mutation is present (penetrance), and potential nature of signs and symptoms (expressivity), is not clear.