Morphological and histological data on the lymphoid system of the bottlenose dolphin, Tursiops truncates, was collected during detailed dissections of 34 animals. Constant Lymph nodes occur in four groups based upon their location and structure: i) somatic, including nodes of the cervical region and pelvic recess; ii) lung-associated, including marginal, diaphragmatic, and hilar nodes; iii) aortic arch nodes, associated with the thymus and thyroid; iv) visceral, including mesenteric, pancreatic, pericolic, and porta hepatis nodes. In addition to these constant node groups, variable Lymph nodes are occasionally found in relation to the thoracic aorta, the kidney, and under the scapula. Somatic nodes have a relatively simple architecture, while the visceral nodes all contain variable amounts of smooth muscle, dependent upon their location. Of the visceral nodes, the mesenteric Lymph node mass is the most richly invested with capsular and trabecular smooth muscle and exhibits a network of muscle fascicles within the organ, implying a contractile function of this mass in the circulation, as well as filtering, of lymph. Lung-associated nodes possess thick capsules with minimal amounts of smooth muscle; drainage of this organ is primarily to the marginal and diaphragmatic nodes. Gut-associated lymphoid tissue includes the dorsal and ventral oropharyngeal tonsils, mucosal aggregates in the colon, and anal tonsils. Aggregates of Lymphoid tissue are also associated with the larynx. Formed organs of the lymphoid system include the thymus and spleen. Based upon morphological observations, it appears that the immune system of Tursiops is fully-developed at birth, similar to the immune system present in ruminants.