OBJECTIVES: To estimate the cost-effectiveness of Reyataz® versus Kaletra® in treatment-naïve HIV-1 patients in Italy. METHODS: For this purpose a life time Markov model was developed with a cycle length of one year. The model included the following health states; 1st, 2nd and 3rd line treatment and within these treatment lines patients could suffer from an MI, stroke or angina. Treatment switch transition probabilities were derived from a 48 week randomized trial and event probabilities were derived from the Framingham risk equations and the 48 week trial. Diarrhea was included as a disutility. Variables that differed between the two treatment arms were pharmaceutical treatment costs, lipid profile, probability to switch 1st line treatment, mortality and incidence of diarrhea. The analysis was conducted from a third-party payer perspective. Direct costs inside the healthcare system were included. Outcomes were reported as cost per (quality adjusted) life year gained. To determine the robustness of the model and the impact of uncertainty, uni- and multivariate sensitivity analyses were carried out. RESULTS: In the base case analysis Reyataz® saved 0.07 [-0.50, 0,83] life years, 0.12 [ -0.31, 0.85 ] QALYs and -€508 [ -€88,264, €19,424 ] costs. The resulting ICER and ICUR were dominant for Reyataz®, e.g. cost saving and more effective. Probabilistic sensitivity analyses showed that Reyataz® has 0.80%, 16.70%, 10.30% and a 72.20% probability to be in NW, SW, NE and SE quadrant of cost-effective scatter plot respectively, and a 94.1% probability to be cost-effective at a WTP of €20,000. The univariate sensitivity analysis showed that the results were especially sensitive to changes in the cost of second and third line treatment and switching treatment probabilities. CONCLUSIONS: The present model suggests that Reyataz® has a favourable cost-effective ratio in the treatment of treatment naïve HIV-I patients. Sensitivity analysis showed that these results were stable.