Background: Establishing irremediability of suffering is a central challenge in determining the appropriateness of medical assistance in dying (MAiD) for patients with a psychiatric disorder. We sought to evaluate how experienced psychiatrists define irremediable psychiatric suffering in the context of MAiD and what challenges they face while establishing irremediable psychiatric suffering. Methods: We conducted a qualitative study of psychiatrists in the Netherlands with experience assessing irremediable psychiatric suffering in the context of MAiD. We collected data from in-depth, semistructured interviews focused on the definition of irremediable psychiatric suffering and on the challenges in establishing irremediability. We analyzed themes using a modified grounded theory approach. Results: The study included 11 psychiatrists. Although irremediable psychiatric suffering is a prospective concept, most participants relied on retrospective dimensions to define it, such as a history of failed treatments, and expressed that uncertainty was inevitable in this process. When establishing irremediable psychiatric suffering, participants identified challenges related to diagnosis and treatment. The main diagnostic challenge identified was the frequent co-occurrence of more than 1 psychiatric diagnosis. Important challenges related to treatment included assessing the quality of past treatments, establishing when limits of treatment had been reached and managing "treatment fatigue." Interpretation: Challenges regarding the definition, diagnosis and treatment of irremediable psychiatric suffering complicate the process of establishing it in the context of MAiD. Development of consensus clinical criteria for irremediable psychiatric suffering in this context and further research to understand "treatment fatigue" among patients with psychiatric disorders may help address these challenges. Registration: This study was preregistered under osf.io/2jrnd.