Objective. To assess whether the cumulative impact of exposure to repeated or chronic stressors, as measured by allostatic load, contributes to the “unhealthy assimilation” effects often observed for immigrants with time in the United States.

Methods. We analyzed data from the National Health and Nutrition Examination Survey, 1988–1994, to estimate multivariate logistic regression models of the odds of having a high allostatic load score among Mexican immigrants, stratified by adult age group, according to length of residence in United States, controlling for demographic, socioeconomic, and health input covariates.

Results. Estimates indicate that 45–60-year-old Mexican immigrants have lower allostatic load scores upon arrival than U.S.-born Mexican Americans, non-Hispanic whites, and non-Hispanic blacks, and that this health advantage is attenuated with duration of residence in the United States.

Conclusions. The findings of our analysis are consistent with the hypothesis that repeated or chronic physiological adaptation to stressors is one contributor to the “unhealthy assimilation” effect observed for Mexican immigrants.