A 25-year-old man who had a complete intramuscular rupture of the long head of the triceps was treated nonoperatively and followed up prospectively for 10 years. The injury occurred after 4 days of white-water kayaking without any direct blow. Strengthening was performed by doing push-ups. Nine years of isokinetic testing revealed that isometric strength was normal, but endurance testing was reduced by 5% to 10%. Ruptures of the muscle belly can occur due to direct trauma or by forced elbow flexion during triceps contraction. From this and the few case reports available it appears that nonoperative treatment is effective and recommended for patients who do not require significant endurance strength in elbow extension. Whether or not the results can be improved by surgical repair is uncertain.