Objective: To compare refraction measured before and after pharmacologic cycloplegia. Methods: This study used preliminary data from the Beaver Dam Offspring Study, which includes adult children of participants in the population-based Epidemiology of Hearing Loss Study of older adults living in Beaver Dam, Wisconsin. Data were available for 5018 eyes of 2529 participants. Refraction was defined by the spherical equivalent (SE), using autorefractor readings. Differences were calculated as the SE after drops were administered minus the SE before drops were administered. Myopia was defined as SE of -1 diopter (D) or less; emmetropia, as SE more than -1 D and less than 1 D; and hyperopia, as SE of 1 D or more. Results: The mean age was 48 years (range, 22-84 years). The mean difference in SE between measurements before and after cycloplegia was 0.29 D (95% confidence interval, 0.28-0.31). The difference decreased with age and varied by refractive status for participants younger than 50 years, with the largest differences observed among young persons with hyperopic refractive errors. Across all age groups, agreement on classifications of refraction was high (84%-92%). Conclusions: Overall, clinically inconsequential differences were observed between SEs beforeandafter pharmacologic cycloplegia, suggesting that cycloplegia may not be necessary in epidemiological studies of refraction in adults.