Objective: This study tested the relationship between cellular immunity and the menstrual cycle in Taiwanese HIV-infected and normal women. Methods: From October 1997 to October 2001, 21 HIV-seropositive women and 30 controls were enrolled in this study. Blood was sampled for hormone profile (estradiol and progesterone) and immunophenotyping with flow cytometry during the follicular and luteal phases. Immunophenotyping included total blood cell count, lymphocyte count, CD4+ cells, CD8+ cells, and their activation markers, including CD25, CD69, HLA-DR, and CD38. Results: The proportion of CD8+ T cells increased during the follicular phase and activating antigens (HLADR and CD38) were elevated on CD8+ T cells of HIV-seropositive women. All these alterations seemed unrelated to the menstrual cycle. Conclusions: The CD8+ T cells were increased and activated in women with HIV infection but these alterations were not affected by the menstrual cycle. Therefore, sex hormones seem not to affect the course of HIV infection.