Lymphadenopathy is one of the most common clinical syndromes requiring differential diagnosis. The spectrum of diseases accompanied by lymphadenopathy is extensive and is within the competence of doctors of various specialties. In most cases, the primary diagnosis is carried out by a general practitioner, who subsequently routes the patient to a specialized specialist. The main condition for a timely diagnosis is knowledge of the causes of lymph node enlargement and a clear differential diagnostic algorithm. In this manual, we tried to structure and outline the main causes of lymphadenopathy, the features of the clinical picture of diseases accompanied by this syndrome, the necessary research methods of high diagnostic significance, as well as the principles of treatment. We hope that our book will help GPs and GPs in their day-to-day work with this category of patients.