Laboratory studies and studies in normal volunteers have suggested a possible adverse interaction between aspirin and ibuprofen. It is thought that ibuprofen prevents aspirin from gaining access to platelet cyclooxygenase. Following the publication of these studies, a number of observational and other studies have been published. We review these studies identified by structured searching of Medline and Pubmed databases. We conclude that on the balance of probabilities that ibuprofen is more likely to interact with aspirin than not. This interaction is more likely in those who take ibuprofen chronically and is more important in those at high cardiovascular risk. Thus, a reasonable strategy might be to advise aspirin takers to avoid chronic ibuprofen.