Os styloideum is an immobile bone protrusion, located on the dorsum of the wrist between the trapezoid, capitate, and the second and third metacarpals, which may be associated with wrist pain. It usually presents in adults after degenerative changes occur. We report a case of a 12-year-old girl who presented with os styloideum. She was evaluated with plain radiographs, bone scintigraphy, and wrist CT. Plain radiographs were initially interpreted as normal. Bone scintigraphy demonstrated focal tracer uptake in the right trapezoid. CT demonstrated an os styloideum fused to the right trapezoid associated with secondary degenerative changes. Os styloideum is a rare cause of wrist pain in children.