A partial posterior interosseous nerve (PIN) paralysis developed in a patient more than 2 decades after having childhood osteomyelitis of the metaphysis of the radius. In previous reports of tardy PIN palsy, the radial head was dislocated (frequently in cases of unrecognized Monteggia fracture-dislocations), causing compression at the arcade of Frohse. In the patient whose case is discussed here, the radial head was located; compression of the PIN at the arcade of Frohse, in combination with traction against inflamed periosteum, likely resulted in the late development of clinical symptoms and signs.