Objective: Developmental models of temperament by environment interactions predict that children’s negative emotionality exacerbates the detrimental effects of risky environments, increasing the risk for pathology. However, negative emotions may have an adaptive function. Accordingly, the present study explores an alternative hypothesis that in the context of high adversity, negative emotionality may be a manifestation of an adaptive coping style and thus be protective against the harmful effects of a stressful environment. Method: Prospective combined effects of negative emotionality and cumulative risk (confluence of multiple risk factors related to poverty) on children’s internalizing and externalizing symptoms and allostatic load, an index of cumulative physiological dysregulation, were assessed in 239 children (46% female, baseline age = 9). Negative emotionality and cumulative risk were assessed at baseline. Internalizing and externalizing behaviors were measured at 4- and 8-year follow-ups. Allostatic load was measured at baseline and both follow-ups using neuroendocrine, cardiovascular, and metabolic parameters. Linear mixed-effect models were used to analyze the prospective associations between negative emotionality, cumulative risk, and the outcomes—allostatic load and internalizing and externalizing behaviors. Results: The combination of high cumulative risk exposure and high negative emotionality was associated with highest levels of internalizing and externalizing behaviors. However, consistent with the alternative hypothesis, negative emotionality reduced the effects of high cumulative risk on allostatic load. Conclusions: In the context of risky environments, negative emotionality may offer some physical health benefits.