This chapter, written for undergraduate medical students and post-graduate doctors in training, presents information on how to manage leg swelling — a case which they are likely to encounter in the future in a general practice setting. It presents the case of a 20-year-old woman with a 2-day history of an increasing feeling of swelling and tenderness in her left lower leg. The most common causes of this type of symptom in a woman of this age who is otherwise healthy would be deep venous thrombosis (DVT), cellulitis, muscle tear or a mass in the thigh pressing on the venous flow from the leg. The chapter provides details of the patients' medical history and the key findings of clinical examination, together with initial investigation results data for evaluation, and helps them develop their skills of clinical reasoning. Key questions then prompt the student to evaluate the patient, and reach a decision regarding their condition and the possible treatment plan.