Objective: To examine mechanisms of the treatment effect for CHOICES, a motivational intervention to reduce risk of alcohol exposed pregnancy (AEP). Grounded in constructs from the transtheoretical model (TTM) and motivational interviewing (MI), the intervention targeted: risk drinking (>4 drinks/day or >7 drinks/week); ineffective contraception; and AEP risk (both behaviors). The experiential and behavioral processes of change (POC), posited to describe the mechanisms through which individual behavior change occurs, were examined. It was hypothesized that each of the targeted treatment outcomes at 9-month follow-up would be mediated by the experiential POC at 3 months, and that these would then be mediated by the behavioral POC at 9 months. Method: Eight hundred thirty women at-risk for AEP were randomized to CHOICES (information plus counseling; IPC) condition (n = 416) or information only (IO) condition (n = 414). Primary outcomes and proposed mediators (POC) were assessed at 3 and 9 months. Path analyses using weighted least squares estimation with mean- and variance-adjusted chi-square statistic were conducted separately for each outcome. Results: Model fit indices indicated good fit, and the indirect effect of treatment on outcome via POC was significant for hypothesized models predicting risky drinking and ineffective contraception. The indirect effect of treatment on AEP risk through POC for ineffective contraception was significant, but the indirect effect of POC for risky drinking was not. Conclusions: These findings support the temporal relationship between experiential and behavioral POC consistent with the TTM. Opportunistic, motivation-based interventions may benefit from directly targeting experiential POC early in treatment and behavioral POC later in treatment.