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Antiretroviral therapy (ART) regimens changes occur frequently among HIV-infected persons. Duration and type of initial highly active antiretroviral therapy (HAART) and factors associated with regimen switching were evaluated in the Multicenter AIDS Cohort Study.Participants were classified according to the calendar period of HAART initiation: T1 (1996–2001), T2 (2002–2005), and T3 (2006–2009). Kaplan–Meier curves depicted time from HAART initiation to first regimen changes within 5.5 years. Cox proportional hazards regression models were used to examine factors associated with time to switching.Of 1009 participants, 796 changed regimen within 5.5 years after HAART initiation. The percentage of participants who switched declined from 85% during T1 to 49% in T3. The likelihood of switching in T3 decreased by 50% (P < 0.01) compared with T1 after adjustment for pre-HAART ART use, age, race, and CD4 count. Incomplete HIV suppression decreased over time (P < 0.01) but predicted switching across all time periods. Lower HAART adherence (≤95% of prescribed doses) was predictive of switching only in T1. In T2, central nervous system symptoms predicted switching [relative hazard (RH) = 1.7; P = 0.012]. Older age at HAART initiation was associated with increased switching in T1 (RH = 1.03 per year increase) and decreased switching in T2 (RH = 0.97 per year increase).During the first 15 years of the HAART era, initial HAART regimen duration lengthened and regimen discontinuation rates diminished. Both HIV RNA nonsuppression and poor adherence predicted switching before 2001 while side effects that were possibly ART related were more prominent during T2.