BACKGROUND: The aim of the present study is to investigate the clinical value and characteristics of peripheral blood lymphocyte subsets in patients with pulmonary tuberculosis (PTB) using flow cytometry. METHODS: The absolute counts of T, CD4+ T, CD8+ T, natural killer (NK), NKT and B lymphocytes in 217 cases of PTB were detected, and the variations in lymphocyte subset counts between different ages and genders and between aetiological detection results and chest radiography results were analysed. RESULTS: In 75.3% of the patients with PTB, six subset counts were lower than the normal reference range, and 44% showed lower-than-normal CD4+ T lymphocyte levels. The counts of T, CD4+ T, CD8+ T and B lymphocytes were significantly lower in patients aged >60 years, and the NKT cell counts were significantly lower in female patients than in male patients. Among the patients with positive aetiological results, 40.8% had reduced CD8+ T counts; these were significantly lower than those in patients with negative aetiological results (P = 0.0295). The cell counts of T, CD4+ T, CD8+ T and B lymphocytes reduced as lesion lobe numbers increased. The counts of T, CD4+ T and CD8+ T lymphocytes were significantly higher in the group with lesions affecting one lobe than in the groups with two to three lobes or four to five lobes, and the counts of B lymphocytes were significantly higher in the group with one lobe and the group with two to three lobes than in the group with four to five lobes. The counts of CD4+ T and CD8+ T lymphocytes were highest in the no cavity group and showed a downward trend with the increase in cavities; the T lymphocyte count was significantly higher in the no cavity group than in the group with five or more cavities (P = 0.014), and the CD8+ T lymphocyte count was significantly higher in the no cavity group than in the group with one to two cavities and the group with five or more cavities (P = 0.001 and 0.01, respectively). CONCLUSIONS: In most patients with tuberculosis, immune function is impaired. The absolute counts of peripheral blood lymphocyte subsets are closely related to the aetiological results and lesion severity in patients with PTB; this could be used as evidence for immune intervention and monitoring curative effects.