The aim of this study was to validate the latest version of the Eating Problem Checklist (EPCL), a tool designed to assess eating-disorder behaviours and psychopathology in patients with eating disorders, session-by-session. The EPCL was completed at baseline by participants with eating disorders (n = 161) and a healthy control group (n = 379) and then administered session-by-session in a subgroup of 75 participants with eating disorders. The EPCL demonstrated good internal consistency, test-retest reliability, and concurrent and criterion validity, and principal axis analysis of the session-by-session data identified two factors ('eating concerns' and 'body image concerns') that accounted for 51.3% of the variance. Furthermore, session-by-session analysis indicated that the EPCL is able to identify specific weekly improvements and/or deterioration in eating-disorder psychopathology. These findings suggest that the EPCL is a valid and reliable self-report questionnaire that provides relevant clinical information regarding weekly changes in eating-disorder behaviours and psychopathology in patients with eating disorders.