Superior adherence to HIV-1 antiretroviral therapy is a mainstay of successful HIV management. Studies performed in the early era of highly active antiretroviral therapy demonstrated the need for > or =95% adherence in order to achieve and sustain viral suppression. High rates of viral suppression have been observed at more moderate levels of adherence with newer antiretroviral regimens. The term 'forgiveness' is being used to describe the ability of a regimen to achieve and sustain viral suppression, despite suboptimal adherence. A variety of pharmacological, viral and host properties determine the level of forgiveness of any specific regimen. As the choice of treatment options continues to expand, forgiveness of non-adherence is likely to emerge as an increasingly important factor in therapeutic decision-making.