Pigmented villonodular synovitis (PVNS) is a rare benign proliferative disorder of the synovium of joints, bursae, and tendon sheaths, with unknown etiopathogeny. It is a synovial hyperplasia related to the formation of villosities and nodules characterized by an intracellular hemosiderin deposit. We present the case of a 27-year-old patient, without previous history, who reported pain and swelling of the right knee. Magnetic resonance imaging evoked the diagnosis of villondular synovitis, particularly on the T2 gradient echo sequence, which was confirmed by histology after synovectomy. This pathology can be diffuse, which is the most frequent form, or local, and affects young adults between the 2nd and 4th decade of life. The most affected location is the knee joint. The diagnosis is based on a combination of radiological criteria, in particular MRI, which identifies the lesion, and histological criteria, which identify the presence of intracellular hemosiderin. The objective of this work is to show the interest and technique of MRI in the diagnosis of villonodular synovitis.