A recent trend in urine drug testing in forensic and clinical toxicology has been the simultaneous determination of different chemical groups of target drugs, which are selected based on their local popularity. Rapid multiple drug analysis, made possible by the use of liquid chromatography-tandem mass spectrometry (LC/MS/MS), has become more widely used, especially in workplace drug testing. Therefore, in the present study, a method for simultaneously analyzing 35 drugs of abuse and relevant metabolites that are most prevalent in Korea, using LC/MS/MS with polarity switching electrospray ionization, was developed and validated. The drugs and metabolites in urine were extracted by using mixed mode strong cation exchange polymeric solid phase extraction cartridges after enzymatic hydrolysis and were then injected into the LC/MS/MS system. The validation results for selectivity, linearity, intra- and inter-assay precision and accuracy for this method were satisfactory, while the results for matrix effects and recovery showed significant variance among the urine samples from different sources. The limits of detection ranged from 0.1 to 10 ng/ml and the limits of quantification were from 1 to 10 ng/ml. To reduce the matrix effects in authentic samples, two different quantitative approaches were compared: quantification using calibration standards prepared by the drug-free pooled urine matrix and quantification using the standard addition. Of these, the latter method was found to be the most suitable. The method developed in this study will be very useful for forensic and clinical toxicology laboratories to adopt for monitoring the inappropriate use of controlled drugs.