It is assumed that the increased incidence of neoplastic pathologies with advancing age is correlated with the immunosenescence and with the altered immune-surveillance. The present study was aimed at evaluating the role of the immunocompetent system and immunosenescence in carcinogenesis. A pool of 99 subjects (38 females, 61 males) has been analyzed in three groups as follows. Group A: 51 elderly subjects with cancer (16 females and 35 males, average age 73.7 +/- 7.5 years). Group B: 24 young subjects with cancer (12 females, 12 males, average age 49.5 +/- 10.3 years). Group C: 24 elderly subjects without any clinical evidence of cancer (10 females, 14 males, average age 74.6 +/- 6.3 years). Hemo-chromocytometric analysis and cytofluorimetric typifying have been performed in all subjects. A decrease of T (CD3+)-lymphocytes has been observed in group A, if compared to group B (P < 0.007), and to group C (P < 0.01), The T (CD4+)-lymphocytes were fewer in group A, than in group C (P < 0.004), and also the NK cells showed the same trend (P < 0.002). The numbers of leukocytes and monocytes increased in group A compared to group C (P < 0.01 and P < 0.004, respectively). Red cell numbers, hemoglobin and hematocrit values were lower in group A than in group B (P < 0.03, P < 0.03, P < 0.01, respectively), and also than in group C (P < 0.007, P < 0.001, P < 0.01, respectively), The results demonstrate that the alterations of the immunocompetent cells, particularly of the T-cell pool, may play an important role in the carcinogenesis of the elderly.