egodystonicityis a distinguishing feature of obsessional thoughts (American Psychiatric Association, 2000) but has not been consistently nor comprehensively defined. These two studies present the development and initial validation of the Ego-Dystonicity Questionnaire (EDQ). A definition of the term egodystonicitywas developed, drawing from existing definitions and theoretical models of obsessive-compulsive disorder (OCD). An item pool was developed and refined through initial testing, the product of which was a 37-item self-report measure. Respondents identify a specific type of thought (e.g., their most upsetting obsession, most upsetting worry) and then answer each item with respect to that thought. In study 1, two nonclinical samples ( N= 278) and one sample of individuals with OCD ( N= 17) were administered the EDQ along with self-report measures of mood, personality, OCD symptoms, and appraisal of obsessional thoughts. A principal components analysis of the nonclinical sample yielded four factors. Scales based on these factors had acceptable internal reliability. The EDQ distinguished between obsessional thoughts and common worries, and individuals in the clinical sample had higher scores than the nonclinical sample. The EDQ showed low to moderate correlations with OCD symptoms, mood, and appraisal of obsessions but was not associated with personality traits such as neuroticism. In study 2, individuals with OCD ( N= 28) completed the EDQ in reference to their most or least upsetting obsession. As predicted, egodystonicity varied according to obsession type. These data indicate that the EDQ is a valid measure with potential for use in understanding and treating obsessional problems.