ECT is efficacious in the treatment of both the depressed and manic phases of bipolar disorder. While ECT is believed to be equally efficacious in the treatment of mixed affective states, to our knowledge there are no empirical studies on this issue. A chart review study was conducted to compare treatment response and clinical course in three groups of patients who received ECT in a general hospital service: bipolar depressed (n = 38), bipolar manic (n = 5), and bipolar mixed (n = 10), diagnosed by DSM-IV criteria. All three groups showed robust response rates, but the number of days of hospitalization was significantly longer in the mixed group (mean 30, SD 19.0 days) compared with the depressed group (mean 19.0, SD 10.9 days, t = 2.4, p < 0.03). There was a trend for the number of ECT treatments to be greater in the mixed compared with the depressed group. These findings indicate that patients with mixed affective states do respond well to a course of ECT, but the longer hospital stays and greater number of ECT treatments suggest that they may be more difficult to treat with ECT than patients with pure bipolar depression or bipolar mania.