The relation between viewing television coverage of a mass disaster and the development of posttraumatic stress disorder (PTSD) is poorly understood. A cohort of New Yorkers without baseline probable PTSD (N = 1787) was assessed 1 year following the September 11, 2001, attacks. The primary outcome was new-onset probable PTSD assessed through a validated scale, and the primary exposure was number of hours of September 11 anniversary news coverage viewed. A total of 99 (5.6%) of participants had developed probable PTSD at the 1-year follow-up. Watching 12 or more hours of September 11 attack anniversary news coverage was associated with a 3.4-fold increased risk of new-onset probable PTSD (p = 0.004). Exposure to television coverage of the September 11 anniversary was associated with new-onset probable PTSD among a cohort of New Yorkers with no probable PTSD at baseline.