Introduction Euthanasia in adults with psychiatric conditions (APC) is allowed in Belgium and impacts a variety of workers in this field, including psychiatrists, psychiatric nurses, psychologists, and support “buddies”. This study examines their perspectives on the appropriateness of the current legal criteria for, and practice of, euthanasia in the context of psychiatry, and their suggestions to properly implement or amend these criteria. Methods Semi-structured interviews were conducted with 30 Dutch-speaking mental healthcare workers who had at least one experience with an APC requesting euthanasia, in Flanders and Brussels (Belgium), between August 2019 and August 2020. Interview transcripts were analyzed through qualitative content analysis. Findings Our study shows that, for these mental healthcare workers, only one of the legal eligibility criteria to assess euthanasia requests by APC (i.e., unbearable suffering) is rather straightforward to interpret. In addition, there was a lack of consensus on what aspects of the Euthanasia Law should be modified and in what way. Conclusions Many mental healthcare workers do not well understand or misinterpret the legal criteria for euthanasia involving APC. Criteria are sometimes defined so narrowly that euthanasia requests by APC are generally deemed ineligible or, alternatively, are stretched to allow for inclusion of cases that go beyond what the Law intended. Our study indicates the need for an authoritative professional code of conduct offering clear advice for Belgian euthanasia practice in the context of psychiatry. It is also recommended that future trainings are standardized, supported by the most important professional associations in the field, and freely available to all who are confronted with euthanasia requests from APC or who offer support to APC who consider euthanasia.