Purpose To describe visual impairment (VI) over a 20-year period and its associations with age-related eye diseases and socioeconomic factors in the Beaver Dam Eye Study. Design Population-based cohort study. Participants Four thousand nine hundred twenty-six persons 43 to 86 years of age participated in the baseline examination phase from 1988 through 1990, and 3721, 2962, 2375, and 1913 persons participated in follow-up examinations each spaced 5 years apart from 1993 through 1995, 1998 through 2000, 2003 through 2005, and 2008 through 2010, respectively. Methods Best-corrected visual acuity after refraction, assessed by the Early Treatment Diabetic Retinopathy Study protocol. Main Outcome Measures Incidence of VI, defined as best-corrected visual acuity of poorer than 20/40 in the better eye in persons with one or both eyes 20/40 or better at the beginning of a 5-year interval, and incidence of severe VI, defined as best-corrected visual acuity of 20/200 or worse in the better eye in persons with one or both eyes better than 20/200 at the beginning of a 5-year interval. Results Overall incidence of VI between examinations (5-year interval) was 1.4% (varying from 0.1% in persons 50–54 years of age to 14.6% in those 85 years of age and older), whereas for severe VI it was 0.4% (varying from 0.0% in persons 50–54 years of age to 6.9% in those ≥85 years of age). The incidence of VI decreased for each period after adjustment for age, from the first 5-year interval between examinations (1988–1990 to 1993–1995) to the fourth and most recent 5-year interval (2003–2005 to 2008–2010; odds ratio fourth interval vs. first interval, 0.53; 95% confidence interval, 0.32–0.87; P = 0.01). This period effect was no longer significant after adjustment for age-related macular degeneration. Age-related macular degeneration remained the leading cause of incident severe VI (54% of eyes with incident severe VI, which was as low as 40% and as high as 57% for specific visits), with no evidence of a trend across visits. The overall frequency of VI correctable with new refraction was 38% of all eyes with VI. Conclusions These data provide population-based estimates that show a high (15%) 5-year incidence of VI in persons 85 years of age and older. Age-related macular degeneration remained the leading cause of severe VI in this population over the 20 years of the study.