Tophaceous gout in a flexor tendon of the hand is a rare form of tenosynovitis. We report on a patient who presented with chronic swelling and restricted movement of his left middle finger. Sonography displayed features atypical of tenosynovitis. The enlarged tendon’s normal fibrillar pattern was replaced by increased echogenicity and heterogeneity. The tendon was highly attenuative to transmitted sound. Subsequent surgery and histology confirmed the diagnosis of tophaceous gout.