Objective: To test the moderating role of the extent of fast-food restaurants in one's immediate environment in the association between mastery and metabolic risk. Higher sense of mastery (perceived control over one's circumstances) has been associated with better metabolic outcomes. Mastery may be instrumental in resisting unhealthful environmental food cues when these become ubiquitous, resulting in a greater health impact of mastery. Methods: Blood samples were obtained from 344 individuals (50% men), aged 18 to 57 years (mean, 34.9 years), sampled from seven census tracts representing the spectrum of census tract-level socioeconomic status and language (French/English) in Montreal. Risk factors based on standards for high-density lipoprotein and total cholesterol, waist circumference, body mass index, triglycerides, and glycated hemoglobin were summed to obtain a cumulative metabolic risk score. Mastery was self-reported, using a validated scale. The proportion of restaurants classified as fast-food within 500 m of participants' residences was determined, using a geographic information system. Main and interactive effects were tested with Poisson regression, accounting for clustering of observations and participants' age, gender, education, and income. Results: Mastery interacted with fast-food exposure in relation to metabolic risk (p =.03). Higher mastery was significantly associated with lower metabolic risk for participants surrounded by a high proportion of fast food (relative risk, 0.80; 95% confidence interval, 0.76-0.84; p <.0001), but not for those living in areas with low proportion of fast-food restaurants (relative risk, 0.94; 95% confidence interval, 0.82-1.08; p =.37). Conclusions: A positive relationship between mastery and lower metabolic risk was most apparent in environments with higher fast-food exposure.