From Herophilus, Aristotle in the 3rd century BC, Aselli, Pecquet, Mascagni to Jossifow and Rouviere the lymphatic system was investigated. Kinmonth and Wallace were the first to study it with lymphangiography. Mediastinal lymph nodes were poorly visualized in high contrast radiography before the seventies; subsequently with the high voltage technique, xerography and signs from mediastinal lines they were better identified. However these procedures were replaced by CT, with which even lymph nodes less than 0.5 cm in size, are recognized. The differentiation between normal and pathologic lymph nodes is based on dimensional, morphologic and densitometric criteria. CT is able to identify typical patterns of inflammatory, systemic and metastatic lymph nodes. On lymphography a great number of signs as gross and dense dotting, foaming, chipping and lacunae are identified, which allow the differentiation of inflammatory, systemic and metastatic patterns. On sonography some nodal characteristics are evidenced as the round shape, hypoechogenicity, absence of hyperechoic medullary line. CT has replaced lymphangiography in the study of abdominal lymph nodes.