ECT is highly effective in major depression. Nonetheless, it remains the most controversial treatment in psychiatry. Controlled trials have shown that ECT technique has a marked impact on short-term efficacy and the magnitude and persistence of cognitive side effects. Yet, there is substantial variation in practice patterns in the community, with many practitioners using techniques that should intensify adverse cognitive outcomes. The short- and long-term impact of this variability in community practice on patient outcomes has never been documented. Furthermore, while predictors of the short-term efficacy of ECT have been suggested, little is known about the patient characteristics that predict effectiveness and cognitive outcomes. Studies of patients receiving ECT have been exclusively restricted to narrowly defined research samples. This study will have two phases. First, in a two- year naturalistic phase, 400 patients with major depression and treated with ECT at four hospitals in New York City will be assessed at preECT baseline, during the week after ECT, and at six-month follow-up. The assessment battery includes measures of diagnosis, symptom severity, objective and subjective cognitive functioning, health-related quality of life, and satisfaction with treatment. This phase will test specific hypotheses about the aspects of treatment technique and baseline patient characteristics that determine short- and long-term outcomes. Based on findings from this naturalistic phase, the 4 hospitals will be ranked according to objective short-term cognitive outcomes. In the second, two-year phase, the two hospitals with the poorest and intermediate cognitive outcomes (ranks 4 and 2) will receive a multi-method intervention designed to improve the quality of practice. The two remaining hospitals (ranks 1 and 3) will serve as controls. The intervention will involve didactics, consultation, on-site supervision by experts, and regular review of patient selection and treatment procedures. Assessment methods will be uniform in-both study phases. The intervention phase, involving 400 additional patients, will be used to demonstrate that clinically significant improvement in patient outcomes can be achieved by use of a multi-method intervention to alter specific aspects of practice. This study will provide new information on (a) the nature and variability of patient outcomes following ECT; (b) the aspects of treatment technique and patient features that determine the variability in outcomes; and (c) the utility of a specific intervention aimed at enhancing patient outcomes.