The longitudinal course of posttraumatic stress disorder (PTSD) over 8-9 years was examined among 16,488 rescue and recovery workers who responded to the events of September 11, 2001 (9/11) at the World Trade Center (WTC; New York, NY), and were enrolled in the World Trade Center Health Registry. Latent class growth analysis identified 5 groups of rescue and recovery workers with similar score trajectories at 3 administrations of the PTSD Checklist (PCL): low-stable (53.3%), moderate- stable (28.7%), moderate-increasing (6.4%), high-decreasing (7.7%), and high-stable (4.0%). Relative to the low-stable group, membership in higher risk groups was associated with 9/11-related exposures including duration of WTC work, with adjusted odds ratios ranging from 1.3 to 2.0, witnessing of horrific events (range = 1.3 to 2.1), being injured (range = 1.4 to 2.3), perceiving threat to life or safety (range = 2.2 to 5.2), bereavement (range = 1.6 to 4.8), and job loss due to 9/11 (range = 2.4 to 15.8). Within groups, higher PCL scores were associated with adverse social circumstances including lower social support, with B coefficients ranging from 0.2 to 0.6, divorce, separation, or widowhood (range = 0.4-0.7), and unemployment (range = 0.4-0.5). Given baseline, exposure-related, and contextual influences that affect divergent PTSD trajectories, screening for both PTSD and adverse circumstances should occur immediately, and at regular intervals postdisaster.