Right unilateral (RUL) ECT is reported to have fewer memory side effects than bilateral (BL) ECT. We compared RUL ECT at eight times the seizure threshold (ST) against BL ECT at 1.5 times the ST. Adults with major depression were randomly assigned to RUL ECT at eight times ST or BL ECT at 1.5 times the ST. Blinded ratings of mood and memory were made before ECT, 1 to 3 days after the final ECT, and at 2 and 4 weeks after ECT. Forty patients received RUL and 37 received BL ECT. The antidepressant response rate was not significantly different for the RUL and BL groups (60% vs. 73%). Sustained antidepressant response, accompanied by recovery from anterograde memory side effects, was seen through the first month with both treatments. Measures of mood and memory were not significantly different for the two groups at any time point. The modest sample sizes of this study do not rule out a type II error in the detection of small but meaningful differences between assigned treatments. Also, the period of post-ECT observation consisted of 1 month of naturalistic treatment. Both RUL ECT at eight times the ST and BL ECT at 1.5 times the ST produce similar mood and memory effects. Both forms of ECT produced acceptable antidepressant response rates and only transient anterograde amnesia. No clear advantage emerged for either form of ECT, and both are justifiable as first-line techniques of ECT.