Triclocarban, N-(4-chlorophenyl)-N'-(3,4-dichlorophenyl)urea, is a polychlorinated phenyl urea pesticide, marketed under the trademark TCC and used primarily as an antibacterial additive in personal care products. Despite its extensive use over several decades, environmental occurrence data on TCC are scarce. This is due in part to a lack of analytical techniques offering the desired sensitivity, selectivity, affordability, and ease of use. This need is addressed here by introducing a liquid chromatography electrospray ionization mass spectrometry (LC/ESI/MS) method allowing for the determination of TCC concentrations in aquatic environments at the ng/L level. TCC was concentrated from aqueous samples by solid-phase extraction, separated from interferences on a C18 column by either isocratic or gradient elution, and detected and identified in negative ESI mode by selectively monitoring the (M - H)- base peak (m/z 313) and its 37Cl-containing isotopes (m/z 315, 317) that served as reference ions. Particulates contained in aquatic samples were extracted and analyzed separately. Accurate quantification was achieved using stable isotopes of TCC and triclosan as internal standards. Addition of 10 mM acetic acid to the mobile phase yielded acetic acid adducts ([M - H + 60]-) that were successfully exploited to boost method sensitivity and selectivity, especially when analyzing challenging environmental matrixes. Method detection limits were matrix dependent, ranging from 3 to 50 ng/L. In 36 grab samples obtained from the Greater Baltimore area, TCC was detected in river water and wastewater at concentrations of up to 5600 and 6750 ng/L, respectively. Raw and finished drinking water did not contain detectable quantities of the pesticide (<3 ng/L). In conclusion, the new LC/ESI/MS method was applied successfully to collect environmental occurrence data on TCC in U.S. water resources. Study results suggest that the bacteriostat and pesticide is a frequent but currently underreported contaminant whose environmental fate and behavior deserve further scrutiny.