Optimal adherence to HIV antiretroviral therapy (ART) is challenging, and racial/ethnic disparities in adherence rates are substantial. The most common reason persons living with HIV (PLWH) give for missed ART doses is forgetting. We took a qualitative exploratory approach to describe, from the perspectives of African American/Black and Hispanic/Latino PLWH, what it means to forget to take ART and factors that influence forgetting. Participants ( = 18) were purposively sampled for maximum variability and engaged in semi-structured/in-depth interviews on HIV/ART management. The analysis took a directed content analysis approach. Participants were mostly male (56%) and African American/Black (79%), between 50 and 69 years old, and had lived with HIV for an average of 21 years. Findings were organised into six inter-related themes: (1) forgetting to take ART was a shorthand description of a complex phenomenon, but rarely a simple lapse of memory; (2) 'forgetting' was means of managing negative emotions associated with HIV; (3) life events triggered mental health distress/substance use which disrupted adherence; (4) historical traumatic events (including AZT monotherapy) and recent trauma/loss contributed to forgetting; (5) patient-provider interactions could support or impede adherence; and (6) intrinsic motivation was fundamental. Implications for HIV social service and health care settings are described.