The safety of attenuated poxviruses in HIV-1-infected individuals is an important consideration in their application as vaccine vectors, first, because new HIV-1 infections may occur in vaccine trials involving persons at high risk of infection and secondly, therapeutic vaccinations are a potential means to enhance virus-specific immune responses once infection has occurred. We administered a candidate modified vaccinia virus Ankara-vectored HIV-1 vaccine, MVA.HIVA, by intradermal injection to 16 chronically infected adults during highly active antiretroviral therapy. Vaccinations were well tolerated and there were no serious adverse events. No breakthrough viraemia occurred after immunisations or throughout follow-up. These data confirm the safety of MVA.HIVA in HIV-1-infected individuals and provide support for further evaluation of MVA-vectored vaccines in prophylactic and therapeutic immunisation strategies.