Vitiligo is an acquired cutaneous disorder characterized by progressive and selective destruction of melanocytes. Although, the exact etiology of vitiligo is still obscure, autoimmunity is strongly implicated in its pathogenesis. The aim of this study was to evaluate the immunological alterations in the peripheral lymphocytes in patients with vitiligo and their possible immunomodulation by narrowband ultraviolet B phototherapy. The study comprised of 44 patients with vitiligo (23 untreated, 21 treated) and 20 normal control subjects who were studied for peripheral blood lymphocytes imbalance using flow cytometry. The percentages of total T-lymphocytes, B-lymphocytes, helper T cells, cytotoxic T cells, activated T lymphocytes, and natural killer cells were evaluated with the use of CD3, CD19, CD4, CD8, CD25, HLA-DR and CD56 monoclonal antibodies, respectively. A statistically significant lower difference in the median values of CD4+ cells (helper T lymphocytes) and CD4+/CD8+ ratio was found between untreated and both of treated and control groups. Natural killer cells (CD3-CD56+) were significantly higher in untreated than the other two groups. On the other hand, activated T-helper cells (CD4+CD25+) were significantly higher in both untreated and treated groups than the control subjects. In conclusion, the reported immunological alterations supported the role of cellular autoimmune mechanisms in the pathogenesis of the disease. Narrowband ultraviolet B phototherapy may enhance cellular immunity in vitiligo patients.