Adult attachment and group process research are emerging areas of research for treating eating disorders. In this study, we examined several aspects of group processes: the weekly growth of group therapy climate, the relationship between group climate growth and outcomes, and the impact of the group on individual experiences of group climate. Further, we assessed the relationship between adult attachment dimensions and these group processes. Women (n = 264) diagnosed with an eating disorder completed attachment scales pre-treatment, eating disorder symptom scales pre- and post-treatment, and group climate scales weekly during treatment. Treatment consisted of a specialized eating disorders group-based day hospital program with rolling admissions. Engaged group climate increased and Avoidance group climate decreased across weeks of treatment. Engaged group climate growth was associated with improved eating disorder symptoms post-treatment. Higher attachment avoidance at pre-treatment was related to lower Engaged group climate at week 1, and was related to a greater impact of the group on the individual's experience of group engagement. Clinicians might improve group processes and outcomes by tailoring interventions to individuals' attachment avoidance when treating women for eating disorders.