Flexor tendon entrapment after a pediatric forearm fracture is a rarely reported complication that is often diagnosed late. Flexor tendon entrapment is more frequently reported after distal forearm fractures, and possible etiologies include fibrosis secondary to hemorrhage at the fracture site and simple entrapment of the muscle belly.This article describes a case of ring finger flexor digitorum profundus entrapment in a 12-year-old boy with a closed both-bone forearm fracture that was treated with closed reduction and intramedullary nail fixation. Preoperatively, the patient had full flexion and extension of all fingers. The entrapment was noted at the first postoperative follow-up when the patient could fully extend the ring finger proximal interphalangeal joint but was unable to concomitantly extend the metacarpal phalangeal joint. Magnetic resonance imaging and ultrasound were obtained to identify the entrapment site. Intraoperatively, a portion of the flexor digitorum profundus musculotendinous junction was entrapped in the fracture site. After release of the entrapment, the patient gained immediate passive range of motion. Subsequently, the hardware was removed, and the patient healed and regained full ring finger function. To the authors' knowledge, this is the only report of isolated ring finger flexor digitorum profundus entrapment after closed reduction and intramedullary fixation of a pediatric forearm fracture. The authors recommend vigilant physical examination of passive and active range of motion of all digital joints with the wrist in flexion and extension before and after bony manipulation.