Nightly ingestion of diazepam, 10mg, alleviated some or all symptoms of intractable sleepwalking in several otherwise healthy adults. Some other patients did not respond as well. The results of this double-blind, crossover study suggest that diazepam is effective for the treatment of adult sleepwalking in some individuals. Data from this study are consistent with uncontrolled case reports of such treatment. Serious side effects or tolerance to the medication did not develop in any of the subjects studied. Other benzodiazepines, which may be more or less effective, remain unstudied. Psychiatric and social histories of these adult sleepwalkers are consistent with earlier work by the authors, which indicates little evidence for an association between uncomplicated sleepwalking and serious psychopathology.