In May 1984, even before People Power and its preceding, rigged Batasan Elections, Diokno had been diagnosed with terminal lung cancer. He obtained a high fever and was brought to the Stanford University Medical Center where he learned of his disease. He had smoked all his adult life. Diokno visited the San Francisco University Hospital to have a brain scan and found a brain tumor. He would return to the motherland and on July 4, 1986, which was the U.S. independence day, had a series of debates with Minister Enrile, convincing him that U.S. bases should be removed from the country. Enrile, who betrayed Marcos and joined the new administration, was inspired by this debate and would later become senator and lead the vote to oust the American military from the country. Diokno returned to the United States on September 3, 1986 for treatment. Eventually after having a transfusion a month later at Manila Doctors Hospital, Diokno decided to stop all treatments and return to his home in Quezon City, to spend his final days reading and writing cases after he shaved his hair off and had experienced a declining line of vision. He continued to work all out for four more months, despite his illness, until his passing on Feb. 27, 1987 at 2:40 a.m.—one day after his 65th birthday. Diokno had spent the last decade of his life making documentaries and speeches, and leading different coalitions and rallies on the streets. His funeral was held at the National Shrine of Our Lady of Mt. Carmel in Quezon City.