Aspirin, nonaspirin nonsteroidal anti-inflammatory drugs (NA-NSAIDs) and acetaminophen all have biologic effects that might reduce the risk of ovarian cancer. However, epidemiologic data on this question are mixed. A population-based, case-control study in western Pennsylvania, eastern Ohio, and western New York State included 902 women with incident epithelial ovarian cancer who were diagnosed between February 2003 and November 2008 as well as 1802 matched controls. Regular use (at least 2 tablets per week for 6 months or more) of aspirin, NA-NSAIDs, and acetaminophen before the reference date (9 months before interview date) was assessed by in-person interview. We used logistic regression to calculate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). The OR for aspirin use was 0.81 (95% CI = 0.63-1.03). Decreased risks were found among women who used aspirin continuously (0.71 [0.54-0.94]) or at a low-standardized daily dose (0.72 [0.53-0.97]), who used aspirin for the prevention of cardiovascular disease (0.72 [0.57-0.97]), who used aspirin more recently, or who used selective cyclooxygenase-2 inhibitors (0.60 [0.39-0.94]). No associations were observed among women using nonselective NA-NSAIDs or acetaminophen. Risk reductions of ovarian cancer were observed with use of aspirin or selective cyclooxygenase-2 inhibitors. However, the results should be interpreted with caution due to the inherent study limitations and biases.