Regulatory T cells (Tregs) blunt uncontrolled immune responses. In advanced human immunodeficiency virus (HIV) infection, the total number of Tregs is decreased, but the proportion of T cells with a regulatory phenotype is highly variable. We studied CD4+CD25+FoxP3+ T cells from patients successfully treated with combination antiretroviral therapy (ART). The proportion of CD4+CD25+FoxP3+ cells transiently increased and then decreased from a median of 13% at baseline to 5.1% at 48 weeks, similar to values in normal subjects. These data suggest that with effective therapy, the regulatory cell numbers normalize, and that the inflammatory signals driving their production may also abate. © The Author 2011. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved.