Psychiatric disorders are among the leading contributors to the global burden of disease. Impaired emotion regulation has been hypothesized to be a transdiagnostic feature of psychiatric disorders, but this has not been proven across all classes of psychopathology. We sought to systematically review and meta-analyze emotion regulation impairment across major psychiatric disorders to determine if impairment is truly transdiagnostic. Selected studies compared healthy controls and individuals with a psychiatric disorder. Emotion regulation was assessed by the Difficulties in Emotion Regulation Scale (DERS), the Emotion Regulation Questionnaire (ERQ), and two other scales. Differences between cases and controls were estimated using Hedges' g for each disorder and scale. 188 studies were included, representing 563 case-control comparisons across 15 diagnoses with 11,201 cases and 9609 controls. For the DERS, case-control differences were large and significant for all 12 disorders analyzed, with effect sizes ranging from 0.94 (95% CI: 0.67-1.21) for bipolar disorder to 2.55 (95% CI: 2.28-2.83) for borderline personality disorder (BPD); BPD had a significantly larger case-control effect size than most other disorders. For the ERQ, use of cognitive reappraisal (an adaptive form of emotion regulation) was reduced in all disorders except panic disorder and use of expressive suppression (a maladaptive form of emotion regulation) was greater in all disorders except ADHD and OCD. Overall, individuals with major psychiatric disorders demonstrated reduced capacity to regulate their emotions across diagnoses and measures, suggesting that interventions which improve emotion regulation could be beneficial to prevent or treat many psychiatric disorders.