Hip synovial cysts are rare. However, in patients with Rheumatoid Arthritis (RA) they present in higher frequency than in general population. Herein, we present an unusual case of a 67-year-old man with RA that presented with unilateral leg oedema and Deep Vein Thrombosis (DVT). Computed tomography (CT) scan revealed a giant cystic lesion adjacent to the right hip joint with longitudinal diameter of 14 cm. Magnetic Resonance Imaging (MRI) confirmed the characteristics of the cyst. Interestingly enough, there was evidence of osteonecrosis of the femoral head. CT guided Fine Needle aspiration (FNA) of the fluid revealed fluid consistency similar to synovial fluid, while it excluded infectious process and malignancy. Patient was finally treated with total hip arthroplasty 3 months after the initiation of low molecular weight heparin (LMWH) in treatment dose.