Red blood cell count (RBC), hemoglobin level (Hb), hematocrit value (Ht), and white blood cell count (WBC) were determined periodically in 499 subjects (274 males, 225 females) aged 60 and over. RBC, Hb, and Ht showed a significant decrease after 5 years in both younger (60-64) and older (65 and over) male groups, and in the female groups except for the Hb level in the older group. Comparison between the younger and older group (cross-sectional study), revealed that the older male group showed lower levels of RBC, Hb, Ht than the younger male group, but the situation was completely the reverse in the females. No significant age-related changes were observed in WBC, but it was significantly higher in both the younger and older male groups than in the female groups. A significant decline with age was observed in both male and female MCV values. On the contrary, from a cross-sectional standpoint, the MCV values in the older female group were higher than those in the younger group. These findings revealed a completely reverse outcome in some parameters, when studied longitudinally and cross-sectionally. Therefore, the data should be evaluated longitudinally to elucidate the real effect of aging. It is pertinent to apply the WHO criteria (male 13 g/dl, female 12 g/dl) to the diagnosis of anemia of elderly people.