Depression and low perceived social support (LPSS) after myocardial infarction (MI) are associated with higher morbidity and mortality, but little is known about whether this excess risk can be reduced through treatment. To determine whether mortality and recurrent infarction are reduced by treatment of depression and LPSS with cognitive behavior therapy (CBT), supplemented with a selective serotonin reuptake inhibitor (SSRI) antidepressant when indicated, in patients enrolled within 28 days after MI. Randomized clinical trial conducted from October 1996 to April 2001 in 2481 MI patients (1084 women, 1397 men) enrolled from 8 clinical centers. Major or minor depression was diagnosed by modified Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria and severity by the 17-item Hamilton Rating Scale for Depression (HRSD); LPSS was determined by the Enhancing Recovery in Coronary Heart Disease Patients (ENRICHD) Social Support Instrument (ESSI). Random allocation was to usual medical care or CBT-based psychosocial intervention. Cognitive behavior therapy was initiated at a median of 17 days after the index MI for a median of 11 individual sessions throughout 6 months, plus group therapy when feasible, with SSRIs for patients scoring higher than 24 on the HRSD or having a less than 50% reduction in Beck Depression Inventory scores after 5 weeks. Composite primary end point of death or recurrent MI; secondary outcomes included change in HRSD (for depression) or ESSI scores (for LPSS) at 6 months. Improvement in psychosocial outcomes at 6 months favored treatment: mean (SD) change in HRSD score, -10.1 (7.8) in the depression and psychosocial intervention group vs -8.4 (7.7) in the depression and usual care group (P<.001); mean (SD) change in ESSI score, 5.1 (5.9) in the LPSS and psychosocial intervention group vs 3.4 (6.0) in the LPSS and usual care group (P<.001). After an average follow-up of 29 months, there was no significant difference in event-free survival between usual care (75.9%) and psychosocial intervention (75.8%). There were also no differences in survival between the psychosocial intervention and usual care arms in any of the 3 psychosocial risk groups (depression, LPSS, and depression and LPSS patients). The intervention did not increase event-free survival. The intervention improved depression and social isolation, although the relative improvement in the psychosocial intervention group compared with the usual care group was less than expected due to substantial improvement in usual care patients.