OBJECTIVES The main objective was to perform a pharmacoeconomic analysis to find out the cost effectiveness of diethylpropion (DEP) with diet and exercise. (DEP+DaE), compared against Diet and Exercise (DaE) in the treatment for obesity from the institutional point of view in Mexico. METHODS Effectiveness data from a mexican clinical trial (Morin, 2007) was used to populate a decision tree model to estimate the cost-effectiveness of DEP+DaE and its comparator DaE. The target population were men and women over 18 years with BMI >30 kg/m2. Principal outcome was the reduction of the Body Mass Index (BMI); benefit was expressed as the percentage of patients who reduced more than 10% of their initial weight. Only direct medical costs were used, such as medications and adverse events; these were obtained from the portal shop by IMSS and also from their unitary costs. To prove the strength of the analysis, deterministic and probabilistic sensitivity tests were performed; all the quantities are expresed in Mexican pesos (MXP) at 2013. RESULTS Both groups lose weight and reduce their BMI. However, these changes were earlier and more pronounced in the (DEP+DaE) group. DeP+DaE presented a significant higher percentage of patients reducing 10% of their intial weight (37% vs 17%, p-value<.05). Incremental cost was $1,455.09 MXP and incremental effectiveness was 20% in reducing the initial weight. The incremental cost-effectiveness ratio of (DEP+DaE) relative to DaE was calculated to be $7,374.07 MXP per additional percentage of reduction suggesting that DEP+DaE is cost-effective compared with DaE as a treatment for obesity in Mexico. CONCLUSIONS The combination of DEP+DaE provides a cost effective improvement to the treatment of patients with a risk profile for obesity in Mexico.