Abstract A sensitive and accurate method was developed for the simultaneous determination of triclosan and triclocarban in sludge and treated biosolids from municipal wastewater treatment plants (WWTPs). The methods involved extraction by pressurized liquid extraction (PLE), followed by sample clean-up on a Oasis HLB solid phase extraction (SPE) cartridge and analysis by liquid chromatography with electrospray ionization and tandem mass spectrometry (LC–ESI-MS/MS). Accurate quantification was achieved by isotope dilution using stable isotopes of triclosan and triclocarban as internal standards. Matrix effects (ME) in samples of spiked biosolids ( n = 5) were evaluated by a standard addition method, and these analyses indicated mean ME values of 79.7 ± 6.7 and 100.5 ± 8.4% for triclosan and triclocarban, respectively; indicating that the sample clean-up method effectively removed interferences. The mean recoveries from the spiked biosolids sample were 97.7 ± 6.2 and 98.3 ± 5 for triclosan and triclocarban, respectively, and the limits of detection (LOD) were 1.5 and 0.2 ng/g (d.w.) for triclosan and triclocarban, respectively. The method was applied to the analysis of triclosan and triclocarban in samples of activated sludge and treated biosolids collected from three WWTPs in Ontario, Canada. These preliminary results indicate that triclosan and triclocarban co-occur in municipal sludge and treated biosolids at concentrations ranging from 0.62 to 11.55 μg/g dry weight for triclosan, and from 2.17 to 5.97 μg/g dry weight for triclocarban.