The Cruzan v. Director, Missouri Department of Health case in 1989 was a significant ruling by the US Supreme Court on the right to die. The case involved Nancy Cruzan, who had been in a persistent vegetative state since 1983 following a car accident. Her parents sought to have her feeding tube removed so she could die naturally but were denied permission by the hospital due to Missouri law requiring clear and convincing evidence of an incompetent patient's wish for withdrawal of life-sustaining treatment. The court ruled 5-4 that competent individuals have a constitutionally protected liberty interest under the Fourteenth Amendment in refusing unwanted medical treatment, but states can apply strict standards when determining whether someone is competent or not and what their wishes are regarding end-of-life decisions if they become incapacitated. This landmark decision affirmed both individual rights over personal medical choices and state interests in preserving human life.

In the Cruzan v. Director, Missouri Department of Health case, Justice Brennan dissented along with Justices Marshall and Blackmun. They argued that an individual's right to refuse medical treatment is a fundamental liberty interest protected by the Constitution. The dissenting opinion stated that this right extends to all individuals, including those who are unable to make their own decisions due to incapacitation or other reasons such as Nancy Cruzan in this case. The justices believed that it was wrong for Missouri law to require clear and convincing evidence of a patient's wish not be kept alive through artificial means when they can't express themselves anymore; instead, they suggested using a standard based on what most reasonable people would want under similar circumstances (the substituted judgment standard). They also criticized the majority for giving too much weight on avoiding potential errors rather than respecting personal autonomy and dignity.