Besides acute inflammatory swelling of a lymph node, acute lymphadenitis, enlarged lymph nodes occur in conjunction with various benign and malignant diseases. Lymphadenopathy can appear in a localized or generalized form and requires further diagnostic measures. Possible causes are primarily infectious, immunological, neoplastic, and metabolic disorders. The medical history and physical examination provide the first clues to the diagnosis. Localized swollen glands often have an infectious etiology so that the first step is to identify the possible focus of infection. Generalized lymphadenopathy is frequently a sign of a hematological systemic disease, particularly in adults. Therefore, in every case of lymphadenopathy persisting for more than 1 month, invasive diagnostic procedures are indicated to rule out a malignant cause. The aim should be to perform a histological analysis; excision of entire lymph nodes is exigent, especially for the work-up of lymphoma. In cases of malignant lymphoma, staging examinations should subsequently be conducted to assess the prognosis and formulate a treatment plan.