A 54-year-old, right-handed man developed spontaneous rupture of his flexor digitorium profundus at the level of the lumbrical. There was no history to suggest rheumatoid arthritis, abnormality of the carpal bones, fractures, or gout. No evidence of any of these disorders was found at the time of surgery. He was treated with a “mini” interposition flexor tendon graft and regained normal motion. Although the cause of his tendon rupture is unclear, we postulate that the blood supply to the tendon at the level of the lumbrical was compromised by an undefined mechanism.