OBJECTIVES: Relative to non-Latino Whites, Latinos have a worse socioeconomic profile but a lower mortality rate, a finding that presents an epidemiologic paradox. This study tested the salmon bias hypothesis that Latinos engage in return migration to their country of origin and are thereby rendered "statistically immortal" and the alternative hypothesis that selection of healthier migrants to the United States accounts for the paradox. METHODS: National Longitudinal Mortality Study data were used to examine mortality rates of the following groups for whom the salmon hypothesis is not feasible: Cubans, who face barriers against return migration; Puerto Ricans, whose deaths in Puerto Rico are recorded in US national statistics; and US-born individuals, who are not subject to either salmon or healthy migrant effects. RESULTS: The sample included 301,718 non-Latino Whites and 17,375 Latino Whites 25 years or older. Cubans and Puerto Ricans had lower mortality than non-Latino Whites. Moreover, US-born Latinos had lower mortality than US-born non-Latino Whites. CONCLUSIONS: Neither the salmon nor the healthy migrant hypothesis explains the pattern of findings. Other factors must be operating to produce the lower mortality.