The evaluation of patients with joint pain begins during the medical history and the physical examination, when the differential diagnosis can often be narrowed to a few likely possibilities. Many patients with joint pain have mild, self-limited symptoms that are best managed conservatively. Exceptions are patients with acute monoarthritis with effusion, in whom septic arthritis must often be excluded by diagnostic joint aspiration. Patients with evidence of active joint inflammation also require prompt evaluation. Laboratory tests for rheumatologic problems lack the sensitivity and specificity to allow their use as screening tools. Laboratory tests are most valuable when used selectively in patients with a clinically significant likelihood of disease. A single test used to rule in or rule out the most likely joint disease is more helpful than a panel of tests used for every patient with joint pain. Testing should aid in determining prognosis or planning treatment.