OBJECTIVES: It is assumed that agencies influence one another but little has been written on the extent of this influence.   This analysis aims to explore how regulatory decisions affect reimbursement decisions within one HIV drug, darunavir.   METHODS: Documents from the FDA, European Public Assessment Report (EPAR), Health Canada, and the Australian Register of Therapeutic Goods together with the reimbursement decisions from France, Scotland, Canada and Australia were analyzed. The clinical trials found in these documents were compared. RESULTS: The FDA approved darunavir ethanolate on June 23, 2006 based on the POWER 1, 2 and 3 clinical trials.  After approval, the FDA also required further reports (to be completed by December 31st 2007) on two Phase III studies, ARTEMIS and TITAN.  Health Canada approved darunavir on July 28th, 2006 and used the POWER studies along with the ARTEMIS and TITAN studies in its decision. The EMA approved darunavir on December 2, 2007 but gave conditional authorization a year earlier. EPAR also used the TITAN and POWER studies to make its decision. The French reimbursement agency used the ARTEMIS and TITAN studies in two recommendations. Scotland and Canada cited the ARTEMIS study in their recommendations.  Australia used the POWER and TITAN studies in two recommendations and the ARTEMIS study in its one negative recommendation, citing an inappropriate comparator for the population under review. CONCLUSIONS: Studies that required further review by the FDA after approval were key in determining regulatory decisions by Health Canada, EMA and Australia.  The reimbursement decisions of France, Scotland, Canada and Australia also relied on these commissioned studies.