The relationship between leisure activities and development of cognitive impairment in aging has been the subject of recent research. We examined television viewing in association with risk of developing Alzheimer's disease (AD) in a case-control study. Given recent focus on the importance of intellectually stimulating activities as preventive measures against cognitive decline, it is important to examine the effects of less stimulating but common activities. Data are from 135 Alzheimer's disease cases and 331 healthy controls. Demographic characteristics and life history questionnaire responses on the number of hours spent on 26 leisure activities during middle-adulthood (ages 40-59) were analyzed. Logistic regression was used to examine the effects of middle-adulthood leisure activities on case vs. control status. Results indicate that for each additional daily hour of middle-adulthood television viewing the associated risk of AD development, controlling for year of birth, gender, income, and education, increased 1.3 times. Participation in intellectually stimulating activities and social activities reduced the associated risk of developing AD. Findings are consistent with the view that participation in non-intellectually stimulating activities is associated with increased risk of developing AD, and suggest television viewing may be a marker of reduced participation in intellectually stimulating activities.