This study examined whether attitudes toward euthanasia vary with type of illness and with the source of the desire to end the patient’s life. The study used a 3 (illness type: cancer, schizophrenia, depression) × 2 (euthanasia type: patient-initiated, family-initiated) between-groups experimental design. An online questionnaire was administered to 324 employees and students from a Australian public university following random assignment of participants to one of the six vignette-based conditions. Attitudes toward euthanasia were more positive for patients with a physical illness than a mental illness. For a patient with cancer or depression, but not schizophrenia, approval was greater for patient-, than, family-, initiated euthanasia. Relationships between illness type and attitudes were mediated by perceptions of patient autonomy and illness controllability. Findings have implications for debate, practices, and legislation regarding euthanasia.