Unexplained episodes of illness occurred among staff in a central operating unit at Marseille’s Hôpital Nord during a period of construction work in August 2005. The nonspecific symptoms, which initially resolved quickly, escalated over time to affect three-quarters of the staff, resulting in the closure of the operating rooms. The combination of multiple factors associated with the construction work in these operating rooms—including ventilation issues, low and uncertain exposure to airborne chemical pollutants, as well as the staff’s legitimate concerns, deteriorating working conditions, and media coverage of these events—led to a self-perpetuating cycle of illness and the development of Sick Building Syndrome. Measures were taken upon the reopening of the central operating suite to improve ventilation and protect staff. No cases of illness were reported in the weeks following the reopening of the suite. (R.A.)