The peripheral blood, spleen, and liver lymphocyte subsets of mice with experimental cheek skin carcinoma were determined. The carcinoma was induced by the topical application of 2% (w/v) 9,10-dimethyl-1,2-benzanthracene (DMBA) to cheek skin twice a week for 12 weeks, and it was examined macroscopically and histopathologically. The composition of lymphocyte subsets (T cells, B cells, CD4+ single-positive [SP] T cells, and CD8+SP T cells) in peripheral blood, spleen, and liver was determined by flow cytometry at 3-week intervals for up to 24 weeks. Spleens and livers were assessed by determining their content of natural killer (NK)T cells. The results showed histopathological progression of the skin lesions from papilloma to squamous cell carcinoma at week 12. Body weight was significantly reduced from weeks 15 to 24, and spleen weight was significantly increased at weeks 21 and 24, but liver weight was not significantly different from the control. The lymphocyte subset composition of peripheral blood showed significant elevation of T cells at weeks 6 and 9, followed by reduced levels at weeks 21 and 24, with significant reduction of B cells at weeks 6 and 9, followed by elevation at weeks 21 and 24. CD4+SP T-cell content was elevated at weeks 6, 9, and 12, and reduced at weeks 21 and 24. CD8+SP T-cell content was significantly reduced at weeks 6, 9, and 12, and elevated at weeks 21 and 24. The composition of the lymphocyte subsets in the spleen was similar to their composition in peripheral blood. The composition of both T and B cells in the liver was significantly different from that in the corresponding control group, but no significant differences were found in either CD4+SP or CD8+SP T cells. These findings revealed that the DMBA-induced cheek skin carcinoma in mice affected not only the lymphocyte subsets in peripheral blood, but the cells in the spleen and liver as well.