Objectives. We analyzed neighborhood heterogeneity in associations among mortality, race/ethnicity, and area poverty. Methods. We performed a multilevel statistical analysis of Massachusetts allcause mortality data for the period 1989 through 1991 (n=142836 deaths), modeled as 79813 cells (deaths and denominators cross-tabulated by age, gender, and race/ethnicity) at level 1 nested within 5532 block groups at level 2 within 1307 census tracts (CTs) at level 3. We also characterized CTs by percentage of the population living below poverty level. Results. Neighborhood variation in mortality across CTs and block groups was not accounted for by these areas’ age, gender, and racial/ethnic composition. Neighborhood variation in mortality was much greater for the Black population than for the White population, largely because of CT-level variation in poverty rates. Conclusions. Neighborhood heterogeneity in the relationship between mortality and race/ethnicity in Massachusetts is statistically significant and is closely related to CT-level variation in poverty.