Introduction: Multimorbidity is the co-occurrence of two or more chronic diseases. The prevalence of multimorbidity increases with age, although it is not limited to elderly individuals. Polypharmacy, understood as the simultaneous use of five or more medications, is closely linked to multimorbidity and increases the risk of adverse drug reactions. Antineutrophil cytoplasmic antibody-associated vasculitis predisposes patients to both multimorbidity and polypharmacy. Managing comorbid chronic conditions requires particular caution in patients with vasculitis. It is essential to account for drug interactions and balance the risk of adverse effects with the need to control disease activity. Case report: This case report describes a 63-year-old patient with vasculitis and multimorbidity admitted to the hospital following a traffic accident. The patient had multiple chronic conditions, including heart failure, coronary artery disease, rheumatoid arthritis, and osteoporosis. Despite treatment, the patient’s condition deteriorated, necessitating a 4-month hospitalization during which the patient, due to the development of infectious complications, including sepsis, required multiple courses of antibiotic therapy and was qualified for chronic haemodialysis due to progressive renal failure. Conclusions: Managing multimorbidity and polypharmacy presents a significant challenge in everyday clinical practice, particularly among older patients, due to the increased risk of adverse drug reactions. An evidence-based therapeutic approach is crucial for treating complex medical conditions.