OBJECTIVES: To investigate whether adherence to antiretroviral treatment (ART) can be explained not only by individual factors but also by health care facilities' characteristics, among a sample of people living with HIV (PLWH) treated with PI-based regimens in Cambodia. METHODS: The ANRS 12276 2PICAM cross-sectional survey was conducted between February 2013 and April 2014 among PLWH followed up in 13 health care facilities. The 1316 patients in this analysis corresponded to 90% of the total number of adult patients treated with 2nd-line PI-based regimens in Cambodia in the study period. A variable indicating whether patients were non-adherent (=1) or completely adherent (=0) was constructed. Health care facilities and individual characteristics were included in a two-level logistic model to investigate their influence on patients' adherence to ART. RESULTS: A total of 17% of participants did not adhere to ART. Patients in health care facilities outside the capital Phnom Penh were six times more likely to be non-adherent than those treated in health care facilities in the capital (OR: 6.15, 95% CI [1.47, 25.79]). Providing psychosocial care (provided by psychologist counsellors and/or full-time coaches) was found to be a structural facilitator of adherence, as the probability of non-adherence fell by 38.5% per each additional psychological worker present in health care facilities (OR: 0.62, 95% CI [0.43, 0.89]). Financial constraints were the main individual factor preventing adherence. CONCLUSIONS: Our results suggest that inefficiencies in health care delivery are detrimental to PLWH health and to the exceptional progress currently being made by Cambodia in response to HIV. Policy makers should focus on increasing the number of psychosocial workers, especially in areas outside the capital.