PURPOSE: To study astigmatism and astigmatism rule by (1) determining changes in prevalence in the United States between 1971 to 1975 and 1999 to 2008 and (2) identifying associations with demographic factors. SETTING: National survey. DESIGN: Retrospective cross-sectional study. METHODS: Participants of the 1971 to 1975 and 1999 to 2008 National Health and Nutrition Examination Survey (NHANES) aged 20 to 74 years representing the U.S population were included. The 1971 to 1975 NHANES measured astigmatism in participants using an algorithm based on presenting visual acuity, lensometry, and objective refraction. Similar methods were implemented using the 1999 to 2008 NHANES data for comparison. Prevalence of clinically significant astigmatism (≥1.0 diopters [D]) was identified, and logistic regression models were used to assess demographic associations with rule of astigmatism. RESULTS: A total of 3371 and 13 10 participants were included from the 1970s and 2000s NHANES. Main outcomes were prevalence estimates of astigmatism and odds ratios estimating associations with demographic characteristics. There was an increase in astigmatism from the 1970s to 2000s (14% [95% CI: 13.2-14.5] vs 24% [22.8-24.6], which was more pronounced in men (12% [10.8-12.7] vs 23% [21.9-24.2]) than in women (16% [14.9-16.8] vs 24% [23.0-25.7]). In adjusted analysis of the 2000s cohort, myopic patients had 8.34 (CI: 7.30-9.54) times greater odds of astigmatism than nonmyopic patients. In the 2000s, there was increased odds of against-the-rule (ATR) astigmatism in men (odds ratio [OR], 1.4; 95% CI: 1.1-1.8) compared with women, in nonmyopic patients (OR, 2.3; 95% CI: 1.7-3.1) compared with myopic patients, and in patients aged 60 to 74 years (OR, 3.7; 95% CI: 2.7-5.1) compared with those aged 20 to 39 years. CONCLUSIONS: There is greater prevalence of astigmatism and ATR astigmatism in 1999 to 2008 compared with 30 years before in the U.S. Factors associated with ATR astigmatism were being male, White, and nonmyopic.