The antimicrobials triclosan (TCS) and triclocarban (TCC) are mass produced chemicals that have been added to personal care products, plastics, and medical supplies since the 1960's and 1950's, respectively. Both chemicals are expected to persist in the environment based on their polychlorinated binuclear aromatic structure, high logarithmic octanol/water partitioning coefficients (logKow), and low aqueous solubility. To address the lack of field data, we investigated the environmental occurrence and persistence of TCS and TCC in the Chesapeake Bay watershed via examination of sediment core fractions (0 to 43cm in depth) representative of environmental conditions near a wastewater treatment plant near the Greater Baltimore area. Antimicrobials were quantified in organic sediment extracts (triplicates), using isotope dilution liquid chromatography electrospray ionization mass spectrometry. Throughout the core, concentrations of TCS and TCC were 0.15 � 0.33 mg/kg and 2.02 � 1.02 mg/kg, respectively. Although both compounds have been produced in similar quantities for over 40 years, the data show that TCC concentrations are 47 � 55 times greater than those of TCS regardless of sediment depth. The occurrence of both antimicrobial compounds at elevated concentrations in historically deposited sediment layers provides evidence for their environmental persistence, particularly for TCC.