The functions of the elbow in 13 cases of ulnar collateral ligament (U.C.L.) tears without gross intraarticular complications were retrospectively evaluated. Ten cases had been surgically repaired, and the remaining three cases were treated conservatively. Follow-up examinations were performed on all of the patients. There was a significant difference in valgus instability between operatively treated patients and conservatively treated patients (operatively treated patients averaged 5.1 degrees, while conservatively treated patients averaged 8 degrees). Two cases of conservatively treated patients complained of elbow joint pain while playing sports or working. Conversely, one of the operatively treated patients complained of numbness in the fifth finger. However, the remaining cases had no symptoms, even while playing sports or working. Valgus instability of the elbow joint results in little inconvenience in daily life, but it is disabling in patients performing heavy labor or vigorous sports.