This chapter, written for undergraduate medical students and post-graduate doctors in training, presents information on how to manage immunization — a case which they are likely to encounter in the future in a general practice setting. It presents the case of a 32-year-old mother of three children. The eldest boy has learning and behaviour problems and has been labelled as having an autism spectrum disorder. Protection against these diseases depends on a combination of group and individual immunity. Serious side effects are very rare, though every surgery offering immunizations should have an anaphylaxis pack ready to hand 'just in case'. 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.