The purpose of this study was to assess the degree of suboptimal antiretroviral therapy adherence to dose, schedule, and dietary instructions and to examine the effects of extra-personal, intra-personal, and inter-personal factors on suboptimal adherence across the three types of instructions. Self-report and clinical data were collected from 193 sexually infected Swedish patients receiving ART. Effects of extra-personal, intra-personal, and inter-personal factors on suboptimal adherence were examined using multivariate logistic regression models. Suboptimal adherence to dose instructions was recorded in 12% of patients. Equivalent percentage for suboptimal adherence to schedule instructions was 37% and for suboptimal adherence to dietary instructions 58%. Anxiety was the only risk factor for suboptimal adherence to dose. Heavy pill burden was a risk factor for suboptimal adherence to schedule. Older age and HIV-related post-traumatic stress disorder (PTSD) symptoms decreased the risk of suboptimal adherence to schedule. No factors investigated had an effect on suboptimal adherence to dietary instructions. To improve adherence to dose and schedule instructions, clinicians caring for patients with HIV should assess and treat anxiety and be alert to HIV-related PTSD symptoms.