A fracture of the sesamoid bone of the hand is rarely seen. In most cases, it is strictly associated with the trauma. The patient complains of a long-lasting, due to unclear diagnosis, painful swelling of the joint with an inability to flex the affected finger. Limited blood supply makes the untreated fracture prone to avascular necrosis. Thus, it is extremely important to make a proper diagnosis early. Bilateral comparing the affected areas with ultrasonography seems to be the method of choice. The treatment is conservative or surgical when needed. We present a case of a radial sesamoid fracture of the second metacarpophalangeal joint without a history of trauma.