This study aimed to analyze the perceptions of nurses working in the Intensive Care Unit (ICU) of a University Hospital in Brazil concerning dysthanasia, orthotanasia and euthanasia and characterize potential implications of their perceptions for care. This quantitative study was carried out with the application of a questionnaire to 27 nurses after approval from the institution's Ethics Committee and authorization from participants were obtained. None of the nurses were able to explain euthanasia, half of them explained dysthanasia, and only a third explained orthotanasia, 65.39% recognized some of these processes in their daily practice, 25.9% believed nurses cannot provide any contribution even being familiar with these concepts and their applicability, 82.36% believed that knowledge of bioethical principles is relevant but only 14.81% were able to mention these principles. The bases of nurses' professional practice were not homogeneous and knowledge about the subject was limited. Orthotanasia, bioethical principles and the delivery of humanized care should be the foundation of nursing care.