test whether (1) young women who subsequently show onset of anorexia nervosa (AN) exhibit persistently lower average premorbid BMI than those who subsequently show onset of bulimia nervosa (BN), binge eating disorder (BED), purging disorder (PD), or no eating disorder; (2) a proximal spike in other risk factors occurs immediately before AN emergence; and (3) psychological and behavioral factors differentiate youth who show persistently low BMI from those who do not.