Combined dislocation of the metacarpophalangeal and interphalangeal joints of the thumb is uncommon, only five cases having been previously reported. In this case report, a previously unreported case characterized by volar-ulnar dislocation of the metacarpophalangeal joint and dorsal dislocation of the interphalangeal joint, associated with a unicondilar open fracture of the proximal phalanx, is presented. Only open reduction for the interphalangeal joint was needed and both (metacarpophalangeal and interphalangeal) joints were treated with K-wire fixation after reduction. Internal fixation of the phalangeal fracture was not performed because of the size of the bone fragment. Although the diagnosis of dislocation of the interphalangeal joint is obvious, a simultaneous dislocation of the metacarpophalangeal joint can be easily overlooked, which is a fact that underlines the importance of this article. It is therefore recommended to examine the whole hand.