An important goal in electroconvulsive therapy (ECT) research is to minimize associated cognitive side-effects while maintaining its high efficacy. This study explored the use of a novel approach, right unilateral (RUL) ECT with an ultrabrief pulsewidth (0.3 ms) (RUL-UB), in comparison with standard RUL ECT. Seventy-four depressed in-patients received RUL-UB ECT at six times seizure threshold, and 22 patients received standard RUL ECT (1.0 ms pulsewidth) at five times seizure threshold. Formal, prospective evaluations of mood and cognitive functioning over the treatment course were done by a rater blinded to treatment condition. Efficacy was maintained using the ultrabrief pulsewidth, with equivalent numbers of responders and remitters to the standard RUL ECT group, although the speed of response was slower. Cognitive outcomes were superior in the RUL-UB ECT group, particularly in the retention of verbal and visual information, as well as in retrograde autobiographical memory.