BACKGROUND Several studies have found that alpha-tocopherol (vitamin E) can effectively treat tardive dyskinesia (TD). A limitation of these trials is their short treatment durations (maximum of 12 weeks), which do not allow us to address the effects of long-term treatment. METHODS To participate, patients had to have TD and be on stable oral medications. The study enrolled 40 patients who received up to 36 weeks of treatment with d-vitamin E (1600 IU per day) or placebo. RESULTS Using the Abnormal Involuntary Movements Scale (AIMS) score (sum of items #1-7) to measure TD severity, the study found a significant difference (3 points) in mean AIMS scores, in favor of vitamin E, starting at 10 weeks of treatment and continuing through the full 36 weeks. We used linear mixed-effects regression to quantify the impact of several covariates, and found that treatment assignment. TD duration, and chlorpromazine equivalents had significant effects on decreasing the AIMS score. CONCLUSIONS The study's finding that vitamin E is effective in treating TD agrees with results from prior studies and provides evidence that the effect may extend to treatment of up to 36 weeks. These findings are in direct contrast to those of VA Cooperative Study #394, a much larger, long-term, multi-site study, conducted by many of the same investigators, in which Vitamin E was not superior to placebo.