STUDY OBJECTIVES: Stressful neighborhood environments are known to adversely affect health and contribute to health disparities but underlying mechanisms are not well understood. Healthy sleep can provide a respite from sustained sympathetic nervous system (SNS) activity. Our objective was to evaluate relationships between neighborhood stress and nocturnal and daytime SNS and parasympathetic nervous system (PNS) activity. METHODS: Eighty-five urban-residing African Americans (56.5% female; mean age of 23.0) participated. Evaluation included surveys of neighborhood stress and sleep-related vigilance, and continuous electrocardiogram (ECG) and actigraphic recording in participants\' homes from which heart rate variability (HRV) analysis for low frequency/high frequency (LF/HF) ratio and normalized high frequency (nHF), as indicators of SNS and PNS activity, respectively, and total sleep time (TST), and wake after sleep onset were derived. RESULTS: All significant relationships with HRV measures were from the sleep period. Neighborhood disorder correlated negatively with nHF (r = -.24, p = .035). There were also significant correlations of HRV indices with sleep duration and sleep fears. Among females, LF/HF correlated with exposure to violence, r = .39, p = .008, and nHF with census tract rates for violent crime (r = -.35, p = .035). In a stepwise regression, TST accounted for the variance contributed by violent crime to nHF in the female participants. CONCLUSIONS: Further investigation of relationships between neighborhood environments and SNS/PNS balance during sleep and their consequences, and strategies for mitigating such effects would have implications for health disparities.