© 2015, Springer Science+Business Media New York. Continuous HIV treatment is necessary to ensure successful combined antiretroviral therapy (cART). The aim of this study was to evaluate the incidence of patient-initiated non-structured treatment interruptions in HIV-infected persons who inject drugs and who received a multidisciplinary comprehensive program, including medical HIV care, drug-dependence treatment and psychosocial support, at a drug outpatient addiction center. Non-structured treatment interruptions were defined as ≥30 consecutive days off cART without medical indication. During a median follow-up of 53.8 months, 37/132 (28 %) patients experienced the first non-structured treatment interruptions. The cumulative probability of cART interruption at 5 years was 31.2 % (95 % CI 22.4–40.0). Current drug use injection ≥1/day (HR 14.77; 95 % CI 5.90–36.96) and cART naive patients (HR 0.35, 95 % CI 0.14–0.93) were predictive factors for non-structured treatment interruptions. HIV care provided at a drug addiction center is a useful strategy to sustain continuous cART, however, drug abstinence is essential for the long-term maintenance of cART.