Tasmanian devil lymphoid tissues (thymus, spleen, and lymph node) from seven animals, including pouch young, juvenile, and adult devils, were investigated using histological and immunohistochemical techniques. Antibodies against the conserved intracytoplasmic portion of CD3 and CD79b (T- and B-cell markers, respectively) and MHC II were used to label immune cells. The thymus from the juvenile devils and the pouch young had CD3+ cells that were primarily located in the medulla of the organ. The spleen consisted of red and white pulp areas with characteristic lymphoid follicles with CD79b+ and MHC II+ cells and nonfollicular T-cell-dominated periarteriolar lymphoid sheaths. Peripheral lymph nodes presented three distinct regions, outer cortex and medulla (both with primarily CD79b+ and MHC II+ cells) and paracortex (mainly CD3+ cells). Tissue architecture and distribution of the immune cells were similar to that seen in eutherian mammals and other marsupials, indicating that the Tasmanian devil has all the structural elements necessary for effective adaptive immunity.