Arthralgia refers to joint pain without swelling, while arthritis signifies joint pain with swelling. In acute monoarthritis, exclusion of septic arthritis is the immediate priority. Acute oligo- or polyarthritis has a broad differential diagnosis (Table 28.1), and if it has persisted >6 weeks, is unlikely to resolve spontaneously and needs urgent referral to a rheumatologist. Assessment of the patient with acute arthritis is summarized in Figure 28.1.