Since the number of centenarians is increasing rapidly in recent years, the establishment of normal ranges in red blood cell (RBC) parameters for healthy centenarians is necessary for diagnostic criteria of anemia. The subjects were 129 centenarians consisting of 27 men (17; healthy, 69; low ADL) and 102 women (33; healthy, 69; low ADL) after excluding centenarians with diseases affecting RBC parameters. The t test was used for statistical evaluation. The mean RBC count for healthy centenarian men was 403 +/- 54.7 x 10(4)/microliters; hemoglobin (Hb) level, 12.4 +/- 1.3 g/dl; hematocrit (Hct), 38.2 +/- 3.9%; MVC, 95.3 +/- 5.3 fl; MCH, 31.4 +/- 2.2 pg; and MCHC, 32.1 +/- 1.1%. Comparable results for healthy centenarian women were as follows: 375 +/- 43.9 x 10(4)/microliters, 11.6 +/- 1.2 g/dl, 36.3 +/- 3.6%, 97.1 +/- 5.3 fl, 31.0 +/- 2.3 pg, and 32.0 +/- 1.3%, respectively. The mean Hb for healthy centenarian women was significantly lower than that for healthy centenarian men. The mean RBC, Hb and hematocrit values for low ADL-centenarian men were lower than the comparable values for healthy centenarian men. Conversely, the mean MCV value for low ADL-centenarian men was higher than that for healthy centenarian men. There was no difference in any RBC parameter between healthy centenarian women and low ADL-centenarian women. In addition, there was no difference in any RBC parameter between centenarian women living in their own homes and those living in old-aged homes. This study demonstrated the normal ranges of RBC parameters for healthy centenarians, and lower RBC, Hb, and Hct values for low ADL-centenarian men.