Objective: The course of anorexia nervosa often includes the emergence of bulimic ymptoms and a crossover to the full syndrome of bulimia nervosa. However, clinicians' ability to predict who will develop bulimia nervosa is limited. The converse phenomenon, crossover from bulimia nervosa to anorexia nervosa, has not been investigated as thoroughly. The authors identified factors that are associated with crossover from anorexia nervosa to bulimia nervosa and from bulimia nervosa to anorexia nervosa. Method: All participants were from the International Price Foundation Genetic Study. Two groups were studied. The first comprised 88 individuals with an initial diagnosis of anorexia nervosa, of whom 32 developed bulimia nervosa. The second included 350 individuals with bulimia nervosa, of whom 93 developed anorexia nervosa. Several variables, including DSM-IV axis I and II disorders and personality traits, were evaluated as potential predictors of crossover. Results: For the majority of affected individuals, crossover occurred by the fifth year of illness. A low level of self-directedness was associated with crossover in both directions. Other factors differed by diagnosis: high parental criticism was associated with crossover from anorexia nervosa to bulimia nervosa, whereas alcohol abuse/dependence and a low level of novelty seeking were associated with crossover from bulimia nervosa to anorexia nervosa. Conclusions: Low self-directedness may be associated with diagnostic instability in general, whereas other specific factors are related to the direction of diagnostic crossover. These results indicate that personality and family characteristics may influence the course of eating disorders and may be informative for planning interventions.