Ganglion cysts are ubiquitous cystic lesions without synovial wall and inconstant communication with the articular cavity. The later must nonetheless always be carefully looked for. We report two cases of ganglion cyst rupture in the retrofemoral fat simulating phlebitis with thigh cellulitis. To the best of our knowledge, this has not been previously reported in the literature. Familiarity with this entity ensures adequate medical diagnosis and management, avoiding unnecessary imaging and laboratory work-up and inappropriate use of anticoagulant and antibiotic.