Self-stigma involves internalized negative evaluation in people with a societally prescribed label (i.e., mental health diagnosis). Thus, measures of self-stigma due to mental illness exclude people without a diagnosis who may negatively evaluate themselves because of their emotions—a process we define as self-invalidation due to emotion. In the current research, we introduced a novel measure of self-invalidation due to emotion distinct from measures of self-stigma due to mental illness and perceived emotion invalidation. After expert review of the item pool (Study 1), and principal component (Study 2) and confirmatory factor analysis (Study 3), a 10-item scale for Self-Invalidation Due to Emotion Scale (SIDES) was developed, with subscales of self-invalidation due to high and low emotional experience. A college student and community sample (Study 4) confirmed test–retest reliability and demonstrated that greater self-invalidation due to high emotional experience predicted greater emotion dysregulation, emotional reactivity and expressivity, and beliefs about emotion uncontrollability. In contrast, greater self-invalidation due to low emotional experience predicted less emotional reactivity and expressivity, and greater beliefs about emotion controllability. Finally, in a community sample of people with a history of mental illness (Study 5), greater self-invalidation due to high but not low emotional experience predicted symptoms of borderline personality pathology and distress regardless of self-stigma due to mental illness or perceived emotion invalidation. The current research supports the SIDES as a psychometrically sound, more inclusive measure of self-stigma, relevant for predicting distress and maladaptive emotional tendencies in people with and without a mental illness. (PsycInfo Database Record (c) 2022 APA, all rights reserved)