Eighty ruptures of flexor tendons, occurring over a thirteen-year period in the fingers in seventy-eight patients, were studied. The tendons involved were the flexor digitorum profundus, flexor digitorum sublimis, and flexor pollicis longus. The majority of ruptures occurred in young patients, suggesting that degenerative changes accompanying aging were not directly responsible for rupture. The force producing the rupture was often slight, indicating that some underlying factors had already predisposed the tendon to rupture. Flexor-tendon ruptures were found to occur most frequently after crushing injuries, lacerations, hyperextension injuries, and as the result of forced flexion against resistance. In 67.9 per cent of the tendons, these ruptures were found at the insertion or musculotendinous junction. In 31.9 per cent, they occurred within the tendon substance. Hyperextension injuries most often produced ruptures at the insertion. Lacerations and crushing injuries were also frequently followed by rupture of a flexor tendon at its insertion or elsewhere within the finger. Ruptures resulting from forced flexion against resistance produced injuries at the tendon insertion, except in those instances where the tensile strength of the tendon had been decreased by pathological changes. In 20 per cent of all the ruptures, pathological changes in the tendon accounted for rupture and in nearly all of the tendons with these changes the ruptures occurred in the palm, carpal tunnel, or wrist. It is emphasized that surgical treatment is often unnecessary. Surgery is essential only when flexor function has been severely compromised or lost.