A 7-year-old Korean boy was referred for a nontender mass in the left arm. He had a 5-year history of a poorly defined painless mass on the medial side of the left elbow. The ultrasonogram of the left arm indicated an ill-defined, lobulating solid mass involving the deep soft tissue layer. The fat-suppressed T2-weighted magnetic resonance image showed a poorly marginated, homogeneous high-signal intensity mass. On further follow-up of 1 year and 6 months, the mass showed no change in size and nature. At surgery, a poorly demarcated inflammatory mass was dissected from a branch of the superficial radial nerve and excised completely. There was no recurrence and any dysfunction, except temporary localized hypoesthesia of the medial aspect of the left arm at the 3.6-year follow-up.