BACKGROUND: Telephone counseling in chronic disease self-management is increasing, but has not been tested in studies that control for quality of medical care. OBJECTIVE: To test the effectiveness of a six-session outpatient telephone-based counseling intervention to improve secondary prevention (behaviors, medication) in patients with acute coronary syndrome (ACS) following discharge from hospital, and impact on physical functioning and quality of life at 8 months post-discharge. DESIGN: Patient-level randomized trial of hospital quality improvement (QI-only) versus quality improvement plus brief telephone coaching in three months post-hospitalization (QI-plus). Data: medical record, state vital records, patient surveys (baseline, three and eight months post-hospitalization). Analysis: pooled-time series generalized estimating equations to analyze repeated measures; intention-to-treat analysis. PARTICIPANTS: Seven hundred and nineteen patients admitted to one of five hospitals in two contiguous mid-Michigan communities enrolled; 525 completed baseline surveys. MEASUREMENTS: We measured secondary prevention behaviors, physical functioning, and quality of life. RESULTS: QI-plus patients showed higher self-reported physical activity (OR = 1.53; p = .01) during the first three months, with decline after active intervention was withdrawn. Smoking cessation and medication use were not different at 3 or 8 months; functional status and quality of life were not different at 8 months. CONCLUSIONS: Telephone coaching post-hospitalization for ACS was modestly effective in accomplishing short-term, but not long-term life-style behavior change. Previous positive results shown in primary care did not transfer to free-standing telephone counseling as an adjunct to care following hospitalization.