Locking of the metacarpophalangeal joint may be produced by bone or soft-tissue abnormality. There is usually a history of trauma to the flexed joint. Previously described bone abnormalities of the metacarpal head consist of marginal osteophyte formation, enlarged impinging sesamoid bone, or irregular contour of the articular surface. Soft-tissue injuries have consisted of linear tears in the collateral ligaments with resultant locking of the torn ligament behind the metacarpal head. In the case reported, a combination of bone and soft-tissue abnormalities produced locking. At operation, there was seen a transverse tear in the volar plate with formation of a pocket that locked around an enlarged articular eminence when the finger was fully flexed.