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.

Osteomesopyknosis may cause chronic, low-grade back pain in the thoracic (middle) and lumbar (lower) regions. It is considered a mild form of osteosclerosis and is usually found in young adults or teenagers. Height and intellect are not affected. Life expectancy in affected people 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.

Osteomesopyknosis is inherited in an autosomal dominant manner. This means that having only one mutated copy of the responsible gene (which has not yet been identified) is enough to cause signs or symptoms of the disorder. When a person with an autosomal dominant condition has children, each child has a 50% (1 in 2) risk to be affected.

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.