Objective: The goal of this study was to assess the effects of training primary care providers (PCPs) to use Motivational Interviewing (MI) when treating depressed patients on providers' MI performance and patients' expressions of interest in depression treatment ("change talk") and short-term treatment adherence.Methods: This was a cluster randomized trial in urban primary care clinics (3 intervention, 4 control). We recruited 21 PCPs (10 intervention, 11 control) and 171 English-speaking patients with newly diagnosed depression (85 intervention, 86 control). MI training included a baseline and up to 2 refresher classroom trainings, along with feedback on audiotaped patient encounters. We report summary measures of technical (rate of MI-consistent statements per 10 minutes during encounters) and relational (global rating of "MI Spirit") MI performance, the association between MI performance and number of MI trainings attended (0, 1, 2, or 3), and rates of patient change talk regarding depression treatments (physical activity, antidepressant medication). We report PCP use of physical activity recommendations and antidepressant prescriptions and patients' short-term physical activity level and prescription fill rates.Results: Use of MI-consistent statements was 26% higher for MI-trained versus control PCPs (P ‫؍‬ .005). PCPs attending all 3 MI trainings (n ‫؍‬ 6) had 38% higher use of MI-consistent statements (P < .001) and were over 5 times more likely to show beginning proficiency in MI Spirit (P ‫؍‬ .036) relative to control PCPs. Although PCPs' use of physical activity recommendations and antidepressant prescriptions was not significantly different by randomization arm, patients seen by MI-trained PCPs had more frequent change talk (P ‫؍‬ .001). Patients of MI-trained PCPs also expressed change talk about physical activity 3 times more frequently (P ‫؍‬ .01) and reported more physical activity (3.05 vs 1.84 days in the week after the visit; P ‫؍‬ .007) than their counterparts visiting untrained PCPs. Change talk about antidepressant medication and fill rates were similar by randomization arm (P > .05 for both). Funding: Funding for this study was provided by the National Institute of Mental Health grant nos. K23MH0829972 and 3K23082997-S1; National Institutes of Health/National Center for Advancing Translational Sciences Colorado CTSI grant no. KL2 TR000156 (to CE).Conflict of interest: none declared. In this study we investigated whether a multifaceted MI training improved (1) PCPs' MI performance during index visits with patients with newly diagnosed depression; (2) subsequent outcomes related to patients' expressed interest ("change talk") in improving this condition; and (3) short-term adherence to treatment 5 (Figure 1). Depression is projected to become the leading cause of disability worldwide by 2030 6 and is often treated, at least in part, in primary care. 7,8 In general, poor depression outcomes in primary care 9 -11 are in part because of pervasive nonadherence to depression treatment, which is ...