Acute monoarthritis has numerous causes, but most commonly is related to crystals (gout and pseudogout), trauma and infection. Early diagnosis is critical in order to identify and treat septic arthritis, which can lead to rapid joint destruction. Joint aspiration is the gold standard method of diagnosis. For many reasons, managing gout, both acutely and as a chronic disease, is challenging. Registrars need to develop a systematic approach to assessing monoarthritis, and be familiar with the management of gout and other crystal arthropathie.