A 41-year-old HIV-positive man who has sex with men (MSM) with a family history of deep vein thrombosis (DVT) presented to the emergency department with an acutely swollen lower limb. The initial clinical diagnosis was of a possible DVT and the patient was anticoagulated. However, investigations subsequently excluded DVT and sexually acquired reactive arthropathy (SARA) was eventually diagnosed. This complication followed an earlier attendance at the emergency department, where proctitis due to lymphogranuloma venereum (LGV) infection went unrecognized. This is the first reported case of LGV infection mimicking a DVT. Prompt recognition and treatment of the initial proctitis may have prevented the development of SARA.