This chapter, written for undergraduate medical students and post-graduate doctors in training, presents information on how to manage weight loss — a case which they are likely to encounter in the future in a general practice setting. It presents the case of a 5-year-old girl who presents with her mother. Her mother has made her come along because she has noticed a marked weight loss in her daughter over the past few weeks. She has also noticed that her daughter seems pale and unwell. 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.