Ictal electroencephalography (EEG) parameters in electroconvulsive therapy (ECT) for depression reportedly correlate with therapeutic response and stimulus dosage, particularly in right unilateral (RUL) ECT. The authors examined ictal EEG parameters as predictors of therapeutic effectiveness in bilateral (BL) sine and pulse wave ECT. A total of 30 consecutive depressed inpatients who had not responded to standard pharmacotherapy were treated using BL ECT given in either sine or pulse wave mode. Ictal EEG parameters (e.g. regularity, postictal suppression) were manually rated by three trained psychiatrists. Polyspike phase duration was significantly longer in sine wave ECT than in pulse wave ECT. Postictal suppression emerged as the only significant predictor of therapeutic outcome when baseline Hamilton Rating Scale for Depression and mode of stimulation were controlled for. Postictal suppression appears to offer a useful predictor of clinical outcome of depression in BL ECT. No EEG parameters were found to be differentially predictive between sine and pulse wave ECT.