AIMS: To quantify the association between treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) and selective cyclooxygenase (COX)-2 inhibitors and hospitalization due to congestive heart failure (CHF); to determine if the risk varies between first and subsequent episodes of CHF. METHODS: We conducted a case-control study of the relationship between recent use of NSAIDs and COX-2 inhibitors and hospitalization with CHF. Cases (n = 530) were patients admitted to hospital with a primary diagnosis of CHF. Controls (n = 1054) were subjects without CHF who were admitted to the same hospitals as the cases. They were frequency matched to cases on the basis of age and sex. Structured interviews were used to obtain information on a number of study factors, including recent use of NSAIDs and COX-2 inhibitors. Relative risks (RRs) were estimated from exposure odds ratios, adjusted for a range of potential confounders. RESULTS: Overall, NSAIDs and COX-2 inhibitors had been taken by 249 (23.6%) controls in the week before admission to hospital. Use of any NSAID/COX-2 inhibitor was recorded in 81/285 (28.4%) first-time cases compared with 38/245 (15.5%) in recurrent cases: difference 12.9% (95% confidence interval 5.9, 19.8) (P = 0.0004). The adjusted RRs for first hospital admission for CHF with different drug exposures were: NSAIDs 1.1 (0.67, 1.83), rofecoxib 1.29 (0.78, 2.13) and celecoxib 1.47 (0.85, 2.53). CONCLUSIONS: We found weak and statistically nonsignificant associations between use of NSAIDs and COX-2 inhibitors and hospitalization with CHF. This low RR is consistent with the results of recently published studies, but not with early studies that found an approximate doubling of risk with use of NSAIDs. The dilution of risk and the significantly lower levels of prescribing for recurrent than for first-time cases of heart failure suggest that prescribing doctors heeded messages that NSAIDs may precipitate CHF in vulnerable individuals, and that they have applied the same message to selective COX-2 inhibitors.