Potentially traumatic events (PTEs) have been consistently associated with posttraumatic stress disorder (PTSD). However, the extent of association and attribution to subsequent disability has varied, with limited studies conducted in urban low-income contexts. This longitudinal study estimated the trajectory of PTSD symptoms up to 7 months after hospitalization and the associated disability level among adult patients who had been hospitalized due to injury. Adult injury patients (N = 476) admitted to Kenyatta National Hospital in Nairobi, Kenya, were interviewed in person in the hospital, and via phone at 1, 2–3, and 4–7 months after hospital discharge. Using latent growth curve modeling, two trajectories of PTSD symptoms emerged: (a) persistently elevated PTSD symptoms (9.2%), and (b) low PTSD symptoms (90.8%). Number of PTEs experienced remained moderately associated with the elevated trajectory after controlling for in-hospital depressive symptoms. Having previously witnessed killings or serious injuries, AOR = 2.32, 95% CI [1.07, 5.05]; being female, AOR = 4.74, 95% CI [4.53, 4.96]; elevated depressive symptoms during hospitalization, AOR = 2.96, 95% CI [1.28, 6.83]; and having no household savings/assets, AOR = 1.28, 95% CI [1.13, 1.44], were associated with the elevated PTSD symptoms trajectory class after controlling for other risk factors. Latent membership in the elevated PTSD trajectory was associated with a significantly higher level of disability several months after hospital discharge, p < .001, after controlling for injury and demographic characteristics. These results underline the associations between in-hospital depressive symptoms, witnessing atrocities, and poverty and an elevated PTSD symptoms trajectory.