OBJECTIVES: Medicament prices restrict the population access to antiretroviral therapy in developing countries. International comparisons indicate Colombia is paying higher ARV prices than comparative developing countries. In addition, its health system is highly decentralized due to the large number of institutional buyers This study addresses the effectiveness of the price control regulatory strategy to lower ARV prices and access to therapy. METHODS: A cross sectional study was performed through a survey designed for the universe of institutional ARV buyers (2005). This included insurers and hospitals linked to the Colombian Health and Social Security System. The survey asked information about VIH/AIDS infected population, individual ARV medicaments transactions, prices, discounts and procurement processes. Descriptive statistics and a multivariate economic model were performed. The answer rate covered over 87% of Colombian population. RESULTS: Study results accounted up to 20,697 persons HIV infected. A 79.8% treatment rate was obtained. Significant differences in the infection rate between both social insurance schemes were identified: Contributive insurance population had a 2.7 higher infection probability than those in the subsidized plan. The lineal regression model showed no significant relationship between the size of the insurance pool and antiretroviral final price to the buyer. Also, there were no price differences between direct purchases to manufacturers and those to distributors. There was a monopolistic tendency with 45% of medicaments offered by a single manufacturer. A market concentration index (Hirsmann- Herfindahl) show that 55% of medicaments purchased in oligopolistic settings. There were no significant price differences from brand-name medicaments and generic drugs in 12 up to 14 ARV medicaments. Finally, there were no significant relation between the regulated price and actual institutional prices. CONCLUSION: Colombia should diversify its regulatory mechanisms and incentives to assure competitiveness, and scale economies in antiretroviral purchases. This approach should face prospective strategies to compensate institutional market fragmentation.