Linda Schneider is a terminally ill northern California woman who suffers from a genetic brain disorder. Her incurable illness causes the brain to atrophy, resulting in deafness, dementia, debilitating seizures, and eventual death. She first experienced symptoms of her illness in July 1994, and during the next few months she was hospitalized three times. At the end of September that year, she suffered a severe seizure and lapsed into a coma.

Linda had previously signed an advance directive stating that she did not want medical treatment to extend her life if she had “an incurable or terminal condition and no reasonable hope of long-term recovery or survival.” Accordingly, when she fell into the coma, her husband, Lee, decided that she should be allowed to die. But doctors did not consider Linda’s condition to...