Doctors have only cared for the world, in various ways; the point, however, is to change it. Imagine you are a distinguished Professor of Medicine, the Rector of one of your country's most garlanded universities. Your students are angry. They have seen fellow students at a nearby university rebel against atrociously poor conditions—overcrowding, incompetent curriculum reforms, and feelings of utter alienation. Tensions are palpable. The air is chilled by the threat of violence. What would you do? Let us not judge. In 1968, at the Sorbonne in Paris, Professor Jean Roche (1901–92), co-discoverer (in 1952) of tri-iodothyronine and one of France's most eminent scientists, made a choice. Was it panic? A miscalculation? The New Yorker called his decision an “unpardonable academic error”. Whatever one's view, the events that followed his decree on May 3 led to the largest conflagration affecting a European nation since World War 2. Roche, a physician and thyroid biochemist, precipitated a national crisis that changed France. His decision to call in riot police to protect the university, its staff and students, was the trigger for unprecedented political upheaval. For 5 weeks, through a combination of street protests and a general strike of about 9 million people, France was paralysed. The consequences, and its meaning 50 years later, deserve reflection. For what happened in May '68 shows how a society reacts when driven to the edge of schismatic social change. “On the night of May 9–10 the Latin Quarter of Paris was a battleground with police releasing tear-gas in an attempt to destroy barricades erected by students…The demonstrating students have widely differing political views; but all insist on the need for university reform.” The Lancet's coverage (May 18, 1968) was sympathetic to the student protests. But in the aftermath of May, progressive voices concluded that the largest mass movement in French history achieved nothing. And so the myths have grown. May '68 was a particularly French expression of the widespread 1960s counterculture. It was a youthful, ultimately playful, revolt. It was spontaneous. It was about free speech. It was poetic (“It is forbidden to forbid”). It was urban. Or, as Raymond Aron put it, May was “the event that turned out to have been a non-event”. It is true that on May 30, 300 000 people marched down the Champs-Elysées to demand order be restored. De Gaulle won. Jails filled. France's Fifth Republic was intact. Students returned to their classrooms. But in more important ways, France—and western Europe—was forever changed. As Daniel Singer wrote in Prelude to Revolution: France in May, 1968 (1970), “the modern state might not be as impregnable as it looks”. May '68 matters not because students failed to seize power. Those few weeks matter because they showed, in Singer's words, “the unsuspected depth of…pent-up discontent”. Medicine played its part too, but, in an echo of Roche's instincts, as a break on the quickening pace of history. Medical students in France in the 1960s came from mostly wealthy families. They were destined for well paid jobs. Although many medical students took part in debates about university reforms in May '68, their discontent was quickly dissipated. As Singer concludes, medical students, “felt no overwhelming professional reasons for reshaping society”. Medicine was the defender of the ancien régime: “many budding doctors…will do no more than grumble”. Despite a victorious conservatism, the legacy of May '68, as Kristin Ross describes in May '68 and its Afterlives (2002), is nevertheless confident, even expectant. Something happened. Students, workers, and farmers refused to be caged in their social categories. Novel and unforeseen alliances among heterogeneous communities were forged. There was a revival of solidarity across classes and ages. A mass movement challenged a fiercely nationalist government. A new era of political engagement was ignited. Resistance to exploitation diffused across an entire nation. From anti-globalisation protests in Seattle to the Occupy movement, from anti-Iraq war campaigns to Arab Uprisings, these are the offspring of May '68. One might judge these mass events to be failures. You would be wrong. Each has shaped the moral conscience of a generation. Each has renewed our sense of social justice. Each has reanimated a dialogue about who we are and what we can be. It all began in Paris in May '68.