BACKGROUND Environmental contaminants ranging from legacy chemicals like p,p'-dichlorodiphenyltrichloroethane (DDT) to emerging chemicals like phthalates are ubiquitous. Research aims/questions: This research aims to examine the presence and co-occurrence of contaminants in human milk and effects of pasteurization on human milk chemical contaminants. METHODS We analyzed human milk donated by 21 women to a milk bank for 23 chemicals, including the persistent organic pollutants (POPs) polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), dichlorodiphenyltrichloroethane (DDT), and dichlorodiphenyldichloroethylene (DDE) isomers that are known to sequester in adipose tissue, along with the current-use and nonpersistent pesticides chlorpyrifos and permethrin, phthalates, and bisphenol A (BPA). Human milk was analyzed raw and pasteurized for these chemicals using gas chromatography-tandem mass spectrometry for the POPs and high-performance liquid chromatography-tandem mass spectrometry for non-POPs. RESULTS Within the different chemical classes, PBDE47, PCB153, ppDDE, and MEHHP (phthalate metabolite) had the highest median concentrations and were observed in all samples. We also observed chlorpyrifos and BPA in all samples and permethrin in 90% of the samples tested. Only two chemicals, chlorpyrifos and permethrin, were susceptible to substantial degradation from pasteurization, a standard method for processing donated human milk. CONCLUSIONS We detected 19 of 23 chemicals in all of our prepasteurized milk and 18 of 23 chemicals in all of our pasteurized milk. Pasteurization did not affect the presence of most of the chemicals. Future research should continue to explore human milk for potential chemical contamination and as a means to surveil exposures among women and children.