Standard pretreatment clinical electroencephalograms (EEGs) were abnormal in 18.6% of 140 consecutive patients with Research Diagnostic Criteria (RDC) endogenous major depression. The patients were randomized to unilateral or bilateral and low- and high-dosage electroconvulsive therapy (ECT) conditions. Clinical features, short-term treatment response, and the rate and timing of relapse were contrasted in patients with normal and abnormal clinical EEG examinations. Psychotic depression was more common among abnormal EEG (61.5%) than normal EEG (38.9%) patients. Otherwise, the two groups were equivalent in a variety of demographic, clinical, and pharmacological variables. Patients with abnormal EEG findings tended to show a poorer rate of response to unilateral ECT, but a strong rate of response to bilateral ECT. Rates and timing of relapse were equivalent in the two groups. Other than the suggestion that bilateral ECT may be preferable in patients with clinical EEG abnormalities, little evidence was found that such abnormalities characterize discrete subgroups or have preductive utility with respect to ECT outcome.