A new method for the simultaneous quantitative determination in human urine of 3-monochloropropane-1,2-diol (3-MCPD), a toxic food contaminant, and its metabolite, 2,3-dihydroxypropyl mercapturic acid (DHPMA), was developed and validated. After urine dilution, the analytes were separated on an Atlantis®dC18 column and quantified by liquid chromatography-tandem mass spectrometry using isotopically labelled internal standards. The limits of quantification (S/N = 10) were 1.90 and 2.21 μg/L for 3-MCPD and DHPMA, respectively. Intra- and inter-day precision were lower than 6 % for each compound. Matrix effects were evaluated. Due to the high sensitivity and good accuracy of the method, 3-MCPD and DHPMA were found in 67 and 100 % of urine samples of healthy subjects, respectively.