BACKGROUND: Nonsteroidal anti-inflammatory drugs (NSAIDs) have been associated with decreased risk of gastric, colorectal, and breast cancer. However, the impact of NSAIDs on the risk of melanoma has been inconsistent. The authors evaluated the association between NSAID use and cutaneous melanoma risk in the Women’s Health Initiative (WHI) Observational Study (OS). METHODS: At study entry, use of aspirin (acetylsalicylic acid [ASA]) and nonaspirin NSAIDs was assessed among 59,806 postmenopausal Caucasian women ages 50 to 79 years. Cox proportional hazards models were constructed after adjusting for participant skin type, sun exposure history, and medical indications for NSAID use among other confounders. RESULTS: During a median follow-up of 12 years, 548 incident melanomas were confirmed by medical review. Women who used ASA had a 21% lower risk of melanoma (hazard ratio, 0.79; 95% confidence interval, 0.63-0.98) relative to nonusers. Increased duration of ASA use (<1 year, 1-4 years, and >/= 5 years) was associated with an 11% lower risk of melanoma for each categorical increase (Ptrend = .01), and women with >/= 5 years of use had a 30% lower melanoma risk (hazard ratio, 0.70; 95% confidence interval, 0.55-0.94). In contrast, use of non-ASA NSAIDs and acetaminophen were not associated with melanoma risk. CONCLUSIONS: Postmenopausal women who used ASA had a significantly lower risk of melanoma, and longer duration of ASA use was associated with greater protection. Although this study was limited by the observational design and self-report of NSAID use, the findings suggest that ASA may have a chemopreventive effect against the development of melanoma and warrant further clinical investigation.