© 2014 Elsevier Ireland Ltd. Background: Cigarette smoking among persons living with HIV (PLWH) is a pressing public health concern, and efforts to evaluate cessation treatments are needed. The purpose of the present study was to assess potential mechanisms of a cell phone-delivered intervention for HIV-positive smokers. Methods: Data from 350 PLWH enrolled in a randomized smoking cessation treatment trial were utilized. Participants were randomized to either usual care (UC) or a cell phone intervention (CPI) group. The independent variable of interest was treatment group membership, while the dependent variable of interest was smoking abstinence at a 3-month follow-up. The hypothesized treatment mechanisms were depression, anxiety, social support, quit motivation and self-efficacy change scores. Results: Abstinence rates in the UC and CPI groups were 4.7% (8 of 172) and 15.7% (28 of 178), respectively. The CPI group (vs. UC) experienced a larger decline in depression between baseline and the 3-month follow-up, and a decline in anxiety. Self-efficacy increased for the CPI group and declined for the UC group. Quit motivation and social support change scores did not differ by treatment group. Only self-efficacy met the predefined criteria for mediation. The effect of the cell phone intervention on smoking abstinence through change in self-efficacy was statistically significant (p<. 0.001) and accounted for 17% of the total effect of the intervention on abstinence. Conclusions: The findings further emphasize the important mechanistic function of self-efficacy in promoting smoking cessation for PLWH. Additional efforts are required to disentangle the relationships between emotional, distress motivation, and efficacious smoking cessation treatment.