Pseudogout, or calcium pyrophosphate deposition disease (CPPD), is characterized by the acute onset of monoarticular joint pain and swelling, usually affecting the large joints. X-rays reveal chondrocalcinosis. Confirmatory data include the positive birefringent, rhomboid-shaped crystals. NSAIDs are effective therapy. Rheumatic fever presents with more striking joint findings in adults than children. A heart murmur should be excluded in adults with polyarthritis, particularly those younger than 30 years. High PMN cell counts may occur in any acute inflammatory condition, such as gout or rheumatoid arthritis. However, very high cell counts, monoarthropathy, and upper extremity involvement should raise suspicions of infection, particularly in the absence of crystals of pseudogout or gout. The Gram stain is positive in a minority of patients with septic arthritis. The serum ANA, ESR, or ASO titer may be useful in evaluating arthropathies.