Emotion regulation (ER) difficulties are observed in eating disorders (EDs). However, few studies have explored ER before and after treatment. The aims are as follows: to explore ER difficulties across ED types and a healthy control (HC) group (Study 1) and to assess pretreatment and post‐treatment changes among ED types (Study 2). In Study 1, adult women with EDs (n = 438) and HC (n = 126) completed an assessment including Eating Disorders Inventory‐2, Difficulties in Emotion Regulation Scale and Symptom Checklist‐90‐Revised. Patients in Study 2 (n = 69) were also reassessed after treatment. All ED types reported worse ER compared with HC (p < .001); also, ER differences were found between ED types. Prospective analyses show ER improvements after treatment (p < .001; |d| = 0.51), especially in patients with bulimia nervosa (p < .001; |d| = 1.03; Reliable Change Index = 9.79) with greater improvement in those with a better treatment outcome (p = .034). In conclusion, emotion dysregulation is a part of all forms of EDs. Furthermore, emotional dysregulation can be modified. ED treatments for anorexia nervosa and binge eating disorder might be enhanced by targeting ER skills. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association.