Mental health professionals stigmatize mental illness, which has significant ramifications for public health and policy. Within this domain, there is a lack of comprehensive research on relative stigma, emotions, and behaviors and an absence of literature that can guide research on these topics. The current study sought to address these limitations. Unstructured interviews were conducted with 22 mental health professionals, and data were analyzed using a grounded theory approach. The current study identified a collection of mental disorders (e.g., borderline personality disorder), stereotypes (e.g., dangerousness), emotion-related responses (e.g., fear), and behaviors (e.g., helping) as being key to the relative stigmatization of mental illness by mental health professionals. The results also suggested that professional context and familiarity with mental illness decrease the stigmatization of mental illness by mental health professionals. These variables and constructs were combined to form a grounded theory of mental health professionals stigmatizing mental illness. The current study has implications for the direction of future research on the stigmatization of mental illness by mental health professionals and interventions that strive to mitigate this type of stigmatization.