['Depression is undertreated in primary care settings. Little research investigates the impact of patient involvement in decisions on guideline-concordant treatment and depression outcomes.', 'The objective of this study was to determine whether patient involvement in decision-making is associated with guideline-concordant care and improvement in depression symptoms.', 'Prospective cohort study.', 'Multisite, nationwide randomized clinical trial of quality improvement strategies for depression in primary care.', 'Primary care patients with current symptoms and probable depressive disorder.', 'Patients rated their involvement in decision-making (IDM) about their care on a 5-point scale from poor to excellent 6 months after entry into the study. Depressive symptoms were measured every 6 months for 2 years using a modified version of the Center for Epidemiologic Studies-Depression (CES-D) scale. We examined probabilities (Pr) of receipt of guideline-concordant care and resolution of depression across IDM groups using multivariate logistic regression models controlling for patient and provider factors.', "For each 1-point increase in IDM ratings, the probability of patients' report of receiving guideline-concordant care increased 4% to 5% (adjusted Pr 0.31 vs. 0.50 for the lowest and highest IDM ratings, respectively, P < 0.001). Similarly, for each 1-point increase in IDM ratings, the probability of depression resolution increased 2% to 3% (adjusted Pr 0.10 vs. 0.19 for the lowest and highest IDM ratings respectively, P = 0.004)."] Is primary care patients ' involvement in decision-making associated with improvement in depression?