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BACKGROUND: Manganese neurotoxicity is well documented in individuals occupationally exposed to airborne particulates, but few data are available on risks from drinking-water exposure. OBJECTIVE: We examined associations of exposure from concentrations of manganese in water and hair with memory, attention, motor function, and parent- and teacher-reported hyperactive behaviors. METHODS: We recruited 375 children and measured manganese in home tap water (MnW) and hair (MnH). We estimated manganese intake from water ingestion. Using structural equation modeling, we estimated associations between neurobehavioral functions and MnH, MnW, and manganese intake from water. We evaluated exposure--response relationships using generalized additive models. RESULTS: After adjusting for potential confounders, a 1-SD increase in [log.sub.10] MnH was associated with a significant difference of -24% (95% CI: -36, -12%) SD in memory and -25% (95% CI: -41, -9%) SD in attention. The relations between [log.sub.10] MnH and poorer memory and attention were linear. A 1-SD increase in [log.sub.10] MnW was associated with a significant difference of -14% (95% CI: -24, -4%) SD in memory, and this relation was nonlinear, with a steeper decline in performance at MnW > 100 µg/L. A 1-SD increase in [log.sub.10] manganese intake from water was associated with a significant difference of -11% (95% CI: -21, -0.4%) SD in motor function. The relation between [log.sub.10] manganese intake and poorer motor function was linear. There was no significant association between manganese exposure and hyperactivity. CONCLUSION: Exposure to manganese in water was associated with poorer neurobehavioral performances in children, even at low levels commonly encountered in North America. Environ Health Perspect 122:1343-1350; http://dx.doi.org/10.1289/ehp.1307918, Introduction Manganese is widespread in the environment [Agency for Toxic Substances and Disease Registry (ATSDR) 2012]. It is an essential element, required for the function of many enzymes and involved [...]