Body checking is common among individuals with anorexia nervosa (AN) and increases risk for dietary restriction. However, no study has examined whether body checking increases the immediate risk for engaging in other harmful weight loss behaviors, or whether this relationship is moderated by person-level traits. The current study utilized ecological momentary assessment (EMA) to examine whether (a) body checking predicted rapid use of weight loss behaviors, and (b) whether eating-related obsessionality/compulsivity moderated this relationship. Women with full or subthreshold anorexia nervosa (N = 118) completed a measure of eating-related obsessionality/compulsivity at baseline, followed by a 14-day EMA protocol during which they reported on body checking and weight loss behaviors (i.e., exercise, self-induced vomiting, laxative use, skipping meals, and increasing fluid intake). In a series of generalized linear mixed models, within-person effects indicated that momentary body checking significantly predicted subsequent meal skipping and using fluids to curb appetite. Between-person effects indicated that individuals who engage in more frequent body checking also engage in a higher frequency of self-induced vomiting, meal skipping, and use of fluids to curb appetite. An individuals degree of eating-related obsessionality/compulsivity did not moderate any of these relationships. Findings highlight body checking as an immediate precursor of dangerous weight loss behaviors among individuals with AN, and underscore the need for clinicians to address body checking during treatment.