The Caribbean region has the world second highest incidence rate of acquired immunodeficiency syndrome. The island of Hispaniola is composed of two sovereign nations: the Dominican Republic and Haiti. Together, they account for more than 85% of HIV/AIDS cases in the Caribbean; and the Dominican Republic alone has approximately 46,000 (33,000-59,000) HIV-1-infected adults and children. Despite this, the magnitude of the genetic variability and evolution of the HIV-1 virus in the Dominican Republic is unclear. In the current study, we analyzed 195 reverse transcriptase (RT) sequences obtained from the Los Alamos HIV database. The data were used to assess the course of the viral epidemic over time in the Dominican Republic, using a coalescent approach. Based on the data, we estimated that the timing of the most recent common ancestor (tMRCA) of local HIV-1 subtype B emerged in 1963, approximately. In addition, the Bayesian analysis provided new information that suggests that the epidemic in the Dominican Republic experienced a significant decrease in relative genetic diversity in the past 2 decades. The results suggest that adherence to antiretroviral therapy, adequate prevention campaigns, and better access to health care may be altering the virus's evolution in the Dominican Republic.