Lithium is a helpful adjunct to patients undergoing ECT. However, only case reports and limited data suggest increase risk of delirium. Thus, this continues to be a controversial issue.In this study, we examine 1) The association and odds of delirium and cognitive problems with ECT and lithium (ECT + Li) combination compared to ECT alone, 2) If positively associated, would this association vary by both type of mood episode and type of disorder?A national sample of 64,728 adult psychiatric inpatients across the US (identified from a total data of about 70 million total discharges annually) was analyzed using linear-by-linear association and logistic regression to assess the odds ratio (OR) for delirium and cognitive impairment for those treated with lithium (N = 158), ECT (N = 64148), or ECT + Li (N = 422) after adjusting for demographics and psychiatric diagnoses.The prevalence of delirium was higher in the ECT + Lithium group (5.7%) vs. ECT only (0.6%) or lithium only groups (0%). Patients managed with ECT + Lithium have 11.7-fold higher odds (95% CI 7.55-17.99, P < 0.001) of delirium compared to ECT alone. In the ECT + Li group, delirium prevalence was 7.8% in unipolar depression, 3.4% in bipolar depressed, 0% in bipolar mania.These results are surprising given the fading concern about delirium association with ECT + lithium combination. The high odds in the combination group warrant clinical caution, use of lower lithium doses (if combinations cannot be avoided), and vigilance regarding early signs of delirium. These results warrant replication in future studies.