Collateral ligament injury of the IP joint of the fingers are common and almost always occurs at the PIP joint. But the rupture of collateral ligament is often miss-diagnosed as sprain and it's seriousness is often underestimated, of such injuries frequently result in prolonged and even permanent disability of the injured fingers. During the period of Sept. 1986 to Aug. 1988, 16 collateral ligament injuries in 15 patients were treated surgically at Holy Family Hospital, Bu Cheon and following results were obtained: 1. Among 15 patients, 14 were male and the age was 32.1 years on an average. 2. The 7 cases had associated injuries in the same fingers. 3. In 6 cases ligaments were ruptured at the proximal attachment, in 5 at the distal attachment, and in 5 at the ligament substance. 4. Average range of joint motion at the final observation was 69.2°. The average flexion contracture was 9.3°, and the average further flexion was 78.5°. 5. The flexion was limited more than the average when the ligament was ruptured at the insertion(66°) and when there were other associated injuries in the same finger(58.1°). The extension was limited more than the average when the ligament was ruptured at the substance(18°) and when patients were over the age of 31 years(12.5°).