Recent evidence suggests that electroconvulsive therapy (ECT) efficacy depends upon both electrode placement and the degree to which stimulus dosage exceeds seizure threshold (T), and not simply on surpassing a minimum seizure duration as has been assumed. In light of these findings and studies reporting ictal electroencephalogram (EEG) differences between bilateral and unilateral ECT, we performed this 19-subject intraindividual crossover study of the effects of dose and electrode placement on the ictal EEG. We found ictal EEG evidence of greater seizure intensity with bilateral than unilateral ECT and with higher dosage (2.25 T) compared with barely suprathreshold stimuli. Seizure duration was not longer with bilateral than unilateral ECT and actually decreased with increased dose. A number of ictal EEG variables separated the unilateral 2.25 T and unilateral T conditions, which reportedly differ in efficacy, and therefore, these EEG measures show promise as markers of treatment adequacy.