Objective: To conduct a formal content analysis of FDA warning letters to manufacturers of pharmaceuticals concerning misleading health outcomes claims. Methods: Two judges formally trained in content analysis procedures critically evaluated warning letters issued by the FDA from 2000 to 2006. An abstraction form was developed to capture information such as company name, product information, type of violation, target audience, and media type. Misleading health outcomes claims were classified into several categories including economic violations, quality of life (QoL) violations, misleading outcomes claims, misleading patient adherence claims, and misleading claims of preference by physicians or patients. The researchers derived a count of all letters and notices and calculated frequency statistics, as appropriate. Disagreements among judges were adjudicated by a third researcher. Inter-rater reliabilities among the judges were determined through kappa statistics. Results: A total of 249 FDA letters to manufacturers were reviewed: 53 (21.3%) warning letters and 196 (78.7%) notices of violations. Misleading outcomes claims accounted for 33 (4%) of the total 809 violations. Misleading health outcomes claims included misleading pharmacoeconomic or cost advantage claim (n=8, 0.9%), misleading claim of improved QoL (n=11, 1.4%), misleading outcomes claims (n=4, 0.5%), misleading patient adherence claims (n=3, 0.4%) and misleading claims of preference by physicians or patients (n=7, 0.9%). Target audience for these violations included health care providers (n=11, 33%) and patients (n=10, 30%). Inter-rater reliabilities among the 2 judges were exceptional, ranging from 0.86 to 1.00. Conclusion: Given that a large portion of drug selection decisions are made on the basis of outcomes data, it is not surprising that the FDA has begun monitoring outcomes research claims to ensure dissemination of accurate and reliable information. The small number of health outcomes violations could be attributed to Section 114 of the 1997 FDA Modernization Act that allows pharmaceutical companies to directly communicate such data to formulary decision-makers.