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A new multiresidue method for the determination of more than 200 pesticides and degradation products with distinct physicochemical properties and 13 polychlorinated biphenyls (PCBs) in water was developed and statistically validated. The method includes solid phase extraction using Oasis HLB cartridges and analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS) and gas chromatography tandem mass spectrometry (GC-MS/MS) for pesticides and GC-MS for PCBs. The method was validated at different concentration levels for pesticides (1, 0.1 and 0.01g L-1) and PCBs (0.1g L-1) (five replicates) by assessing the following parameters: accuracy, precision, limit of quantification and linearity. Calibration curves were established for all analytes and regression analysis was performed at 95% confidence level. About 4.1% of the analytes had a recovery less than 60%, 5% from 60 to 70%, 84% from 70 to 120% and 6.8% from 120 to 140%. Acrinathrin had the lowest recoveries among all analytes studied both in LC and GC systems. In terms of pesticide class, lowest recoveries were for pyrethrins, aryloxyphenoxypropionic acids, cyclodienes and organochlorines. For PCBs, recovery ranged from 45.4% for deca-substituted PCB-209, to 105% for di-substituted PCB-11. The developed method was applied for the determination of pesticide residues in 73 samples of groundwater intended for irrigation purposes from three regions in Greece: (1) Prefecture of Messinia, Peloponesse; (2) Prefecture of Heraklion, Crete; and (3) Prefecture of Lasithi, Crete, during the period of November 2011 to November 2013. Eleven samples were found positive for pesticide residues, with ethalfluralin being the most frequently detected pesticide.