Treatment outcome studies demonstrate that day-hospital programs are effective in the treatment of eating disorders. Few descriptions are available on the specifics of treatment, particularly the process of therapy. The group therapy modality is thought to provide important therapeutic benefits. The present study aimed to examine the association between individuals' cohesion to the group, attendance and early treatment response at a day-hospital program for eating disorders. A total of 36 women were recruited upon admission to the Eating Disorders Day Treatment Program (EDDTP). Cohesion and motivation were assessed at the beginning of treatment. Treatment response was measured after 12-weeks and attendance was recorded daily. Participation in the day-hospital program was associated with improvements in eating disorder symptoms and related pathology, consistent with international treatment outcome studies. Compatibility, which is a distinct aspect of cohesion, was found to be associated with attendance and treatment response. Clinical implications pertaining to the findings are discussed and areas of future research suggested. (Contains 3 tables.)