Background Despite solid research there remains a large group of patients with eating disorders who do not recover. Emotion dysregulation has been shown to be a feature in the different eating disorders. A manualized group intervention developed in Sweden, the Affect School, aims to enhance emotional awareness and the ability to perceive and express emotions. Aim This study aimed to test the hypothesis that participation in the Affect School as a complement to ordinary eating disorder treatment would enhance awareness and regulation of emotions and reduce alexithymia and cognitive eating disorder symptoms in a sample of patients with eating disorders at a Swedish specialized outpatient clinic. Method Forty patients with various eating disorders were randomized to either participation in the Affect School as a supplement to treatment as usual (TAU), or to a TAU control group. Participants were assessed with the Eating Disorder Examination Questionnaire, the Deficits in Emotion Regulation Scale-36, and the Toronto Alexithymia Scale-20 at start, end of intervention, and at the 6- and 12-month follow-ups. Results No significant differences were observed post-treatment but Affect School participants had improved significantly more than controls on eating disorder cognitions and behaviours and emotion dysregulation at the 6- and 12-month follow-ups and had significantly less alexithymia at the 6-month follow-up. Conclusion Difficulties with emotion recognition and/or regulation can complicate fulfilment of personal needs and obstruct communication and relationships with others. The present study indicates that adding Affect School group sessions to regular treatment enhances emotional awareness and emotion regulation and decreases eating disorder symptoms and alexithymia. Plain English summary Patients with eating disorder diagnoses have described problems with emotional management, for example: lower emotional awareness and difficulties in using adaptive emotional regulatory strategies compared to people without eating disorders. It has been suggested that interventions aiming at enhancing emotional awareness and acceptance would be beneficial in treatment. In the present study we explored whether adding the Affect School to regular treatment would enhance awareness and regulation of emotions and decrease eating disorder symptoms. Forty women with an eating disorder were randomly allocated to either an additional participation in a group treatment for 8 weeks or usual treatment only. The treatment contained education on different affects such as joy, fear, interest, shame, anger, disgust, and worry. The education was followed by discussions on own experiences. Participants filled in self-assessment forms that measured eating disorder symptoms, emotional recognition, and emotion regulation before the start and at the end of the group treatment, and after 6 and 12 months respectively. The results when comparing the two groups suggested that the Affect School could be an effective additional treatment. Participants in the Affect School improved their scorings but the change took time and did not show until at the 6- and 12 months follow-ups.