An unusual case of localized pigmented villonodular synovitis of the ankle joint in a 3-year-old boy is described. The child was brought to the hospital because of abrupt onset of pain and joint effusion. A soft tissue mass eroding the talar dome was seen in roentgenograms. Exact diagnosis was established by excisional biopsy. Curettage of the lesion resulted in healing without recurrence at 10-year follow-up examination.