Change in physiologic corneal astigmatism due to aging was studied. A series of 868 cases (1,660 eyes) was evaluated. These eyes were divided into 6 groups by age; A) below 40 years, B) in the 40's, C) in the 50's, D) in the 60's, E) in the 70's, and F) over 80. Corneal astigmatism was examined with an autokeratometer. In Group A, 88.5% had with-the-rule astigmatism (WTR), whereas only 3.7% had against-the-rule astigmatism (ATR). The cylindrical diopter (CD) of WTR was 1.29 +/- 0.73 D, which was significantly the largest among the groups. In Group C, WTR decreased to 55.9% and ATR increased to 22.9%. The CD of WTR also decreased to 0.85 +/- 0.47 D. In Group E, WTR was 31.4% and ATR was 49.3%. The CD of ATR increased to 0.88 +/- 0.70 D. In Group F, WTR was 19.9%, whereas ATR was 65.9%. The CD of ATR was 1.48 +/- 0.88 D, which was the largest among the groups. As such, WTR was dominant at younger ages, and ATR increased with aging at older ages. The CD of WTR decreased, and ATR increased, with aging.