Racial and ethnic disparities in asthma health outcomes have been increasing in the United States. These disparities are so striking that researchers and public health officials have issued a call for action to understand why this is occurring. Compared with non-minority children, minority children use controller medication less often, have less continuity of care, and visit emergency departments more frequently. Especially noteworthy has been the increasing prevalence of asthma among Latino (primarily Puerto Rican) children. Individuals of Mexican and Puerto Rican origin constitute 73% of the Latino population in the U.S. and although these two groups share similar historical origins and cultural values, significant heterogeneity exists. Researchers have tended to study Latinos as a single group but recent descriptive asthma research has confirmed differences among Latino subgroups related to prevalence, mortality and morbidity, illness beliefs, and asthma healthcare practices. Puerto Rican children exhibit the highest rates of asthma prevalence and mortality among all ethnic groups while Mexican children have the lowest rates. Asthma disproportionately affects Puerto Rican children: the adjusted odds ratio for lifetime diagnosis compared to non-Latino white children is 2.33. Genetic, environmental, healthcare system and provider factors cannot totally explain the difference in outcomes between these two groups.