Abstract. Angiofibroma of soft tissue (AFST) is an extremely rare soft tissue neoplasm that typically presents as a slow-growing, painless mass in the extremities. The present study reports an unusual case of an intra-articular AFST occurring in the left knee of a 23-year-old female. Physical examination revealed a 3-cm, relatively mobile, elastic-hard, non-tender mass. Magnetic resonance imaging detected an intra-articular soft tissue mass with iso-signal intensity relative to skeletal muscle on T1-weighted sequences and heterogeneous high signal intensity on T2-weighted sequences. Contrast-enhanced fat-suppressed T1-weighted sequences demonstrated strong peripheral enhancement of the mass. An arthroscopic excision of the mass was performed. Histologically, the tumor was composed of spindle-or oval-shaped cells in a fibromyxoid stroma with a prominent vascular pattern. Immunohistochemically, the tumor cells were diffusely positive for vimentin and CD163 and focally positive for CD68, desmin and estrogen receptor. Based on these findings, the tumor was diagnosed as an AFST. The patient had no evidence of local recurrence within 9 months of follow-up. To the best of our knowledge, this is the first case of intra-articular AFST managed successfully with arthroscopic excision.