Binge eating disorder (BED) is characterized by a bulimic binge eating pattern without the compensatory behaviors of purging or laxative abuse. It is often associated with obesity. The treatment response characteristics are more like bulimia than other forms of obesity. We have shown the opiate antagonist naltrexone to attenuate bulimia nervosa in controlled clinical trials. We report here a response to naltrexone in a subject with BED similar to that previously reported for the larger population of bulimic subjects. Three consecutive periods of drug, placebo and double dose drug were used, with the order of the first two periods double blind until after the data analysis. Symptoms were reduced in the naltrexone compared to placebo period. Statistical significance was demonstrated using time series analysis for this 'n of one' study. Psychotherapy was carried out throughout all periods. Naltrexone plus psychotherapy may be more efficient than psychotherapy alone.