The proximal phalangeal base is the most commonly fractured hand bone in children. Such fractures are rarely reported to be irreducible as a consequence of flexor tendon entrapment. A 12-year-old male sustained a malunited base fracture of the proximal phalanx of the small finger on the right hand and was unable to flex the finger. 6 weeks ago he was treated with closed reduction and percutaneous K-wire fixation, at another hospital. In a subsequent operation, it was found that the flexor tendon was entrapped at the fracture site. Flexor tenolysis and realignment of the fracture and internal fixation with K-wires were performed. The patient could perform his work without discomfort in his hand and a normal range of motion was possible in the small finger 12 months after the operation.