A simple, rapid and sensitive liquid chromatography–tandem mass spectrometric (LC-MS/MS) assay method has been developed and validated for simultaneous quantification of sitagliptin and simvastatin in human plasma. Carbamazepine was used as an internal standard (IS). The analytes and IS were extracted from the human plasma by liquid–liquid extraction technique. The reconstituted samples were chromatographed on an Alltima HP C18 column using an isocratic solvent mixture [acetonitrile–5 mm ammonium acetate (pH 4.5), 85:15 (v/v)] at a flow rate of 1.0 mL/min. Method validation was performed as per Food and Drug Administration guidelines and the results met the acceptance criteria. The calibration curves obtained were linear (r2 ≥ 0.99) over the concentration range of 0.10–501 and 0.05–105 ng/mL for sitagliptin and simvastatin, respectively. The results of the intra- and inter-day precision and accuracy studies were well within the acceptable limits. Both the analytes were found to be stable in a battery of stability studies. The method is precise and sensitive enough for its intended purpose. A run time of 3.0 min for each sample made it possible to analyze more than 300 plasma samples per day. The developed assay was successfully applied to a pharmacokinetic study in human volunteers. Copyright © 2012 John Wiley & Sons, Ltd.