Pharmaceuticals and personal care products (PPCPs) constitute a class of chemicals of emerging concern due to the potential risks they pose to organisms and the environment, even at low concentrations (ng/L). Recent studies have found that PPCPs are not efficiently removed in secondary wastewater treatment plants (WWTPs). This study has: (1) simultaneously investigated the occurrence of sixty-one PPCPs using solid phase extraction and high-performance liquid chromatography-tandem mass spectrometry, (2) evaluated removal efficiencies of target PPCPs in six WWTPs that discharge effluents into major Taiwanese rivers, and lastly (3) examined matrix interference during analysis of target PPCPs in water samples. The twenty target PPCPs were chosen for their high detection frequencies, high influent concentrations, and stability during wastewater treatment processes. Caffeine and acetaminophen were detected at the highest concentrations (as high as 24,467 and 33,400 ng/L) and were effectively removed (both >96%); other PPCPs were detected in the high ng/L range but were not effectively removed. Matrix interference (by ion suppression or enhancement) during the analysis resulted in underestimation of the removal efficiencies of erythromycin-H(2)O, cefazolin, clarithromycin, ibuprofen, diclofenac, clofibric acid and gemfibrozil.