Lymphadenopathy can occur in any age group, in symptomatic or asymptomatic patients, and in a single site or at multiple sites. Lymphadenopathy is associated with numerous disorders. An abnormal lymph node may be observed or palpated by the patient, found by a health care worker, or discovered through radiologic evaluation. Lymphadenopathy may be a part of a complex case presentation, or the clinical cause may be straightforward. Patients with potentially curable malignant disorders may have lymphadenopathy as the first sign of their disease. This review of lymphadenopathy summarizes general considerations, discusses which patients might be considered for biopsy, reviews which nodes are most likely to be diagnostic, outlines initial diagnostic considerations on a region-by-region basis, and reviews a broad differential diagnosis for adenopathy.