OBJECTIVE: To investigate the quantity and quality of Patient-Reported Outcome (PRO) claims in pharmaceutical advertisements in two Thai medical journals. METHODS: A retrospective review of all pharmaceutical advertisements in the 2004 issues of 2 Thai medical journals(Clinic and Pharmatime) was performed by 3 trained pharmacists.Two reviewers independently reviewed the advertisements. If the reviewers disagreed the final decision was made by the third reviewer. All distinctive pharmaceutical advertisements were classified into claim advertisement or reminder advertisement. PRO claims and economic claims were also identified. Then, the advertisements were categorized according to their reference statuses. Finally, the reviewers evaluated whether the cited references provided substantial evidence to support the claims. RESULTS: From 183 advertisements reviewed, there were 48 distinctive advertisements. Forty-five (0.94%) and three (0.06%) of the advertisements were classified as claim advertisement and reminder advertisement, respectively. Nineteen (0.42%) of the claim advertisements contained PRO claims while two(0.04%) of the claim advertisements contained economic claims. The result indicated that only 16 (0.36 %) of the claim advertisements cited at least one published article retrievable from Medline as a reference, while the remaining 24 (0.49%) contained no reference or cited package insert or non-published data on file as references. When looking closely at PRO claims, it was found that 12 (0.63%) of the PRO claims were misleading because the outcomes stated in the claims were not supported by the given references. In addition, there was not sufficient evidence to support all 2 economic claims. CONCLUSIONS: More than half of the PRO claims were misleading. Practitioners should be cautions in assessment of PRO claim advertisements in medical journals. There is also a substantial need for more rigorous regulation of PRO claims.