Injuries involving the midtarsal joint, which are frequently misdiagnosed, have been studied to clarify the mechanism, classification and treatment. The necessity for routine antero-posterior, lateral and oblique radiographs is emphasised. Seventy-one injuries have been classified according to the direction of the deforming force:medial, longitudinal compression, lateral, plantar and crush types are described. Included in the medial and lateral types is a hitherto undescribed tarsal rotation or "swivel" injury. The mechanism whereby longitudinal compression causes fractures of the body of the navicular is described, and two varieties having different prognoses are defined: one due to purely longitudinal compression and the other due to longitudinal compression with a medial component. The results of treatment have been assessed clinically and radiologically. Reduction, open if necessary, with internal fixation, is recommended for displace fractures: primary arthrodesis is not indicated. For severe persistent symptoms from medial and longitudinal force injuries triple arthrodesis is recommended, and from lateral force injuries, calcaneo-cuboid arthrodesis.