This chapter, written for undergraduate medical students and post-graduate doctors in training, presents information on how to manage tiredness — a case which they are likely to encounter in the future in a general practice setting. It presents the case of a 25-year-old woman who consults infrequently. She says that she has been feeling tired off and on over the past 4 months and a little bit down. Specifically, apart from the tiredness and mild depression she does not have symptoms of dry hair and skin, constipation, weight gain or feeling unusually cold, other symptoms suggestive of an underactive thyroid. 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.