The present study examined both the intraindividual relationship between alliance components (task, goal, and bond) and subsequent posttraumatic stress disorder (PTSD) symptoms over the course of therapy and the interindividual relationships between the initial level of the alliance components and overall PTSD outcome. PTSD patients (n = 65) were randomized to either standard prolonged exposure, which includes imaginal exposure (IE) to the traumatic memory, or modified prolonged exposure, where imagery rescripting (IR) of the memory replaced IE as the imagery component of prolonged exposure in a 10-week residential program. They were assessed repeatedly (weekly) on alliance and PTSD symptom measures. The centering method of detrending (Curran & Bauer, 2011) was used to separate the variance related to the intraindividual process of change during treatment (within-person component) from the variance related to initial individual differences (between-person component). The hypothesis of a negative within-person effect of the alliance components agreement about the tasks of therapy and bond on subsequent PTSD symptoms was supported for the component task agreement. As expected, this effect was stronger in IE than in IR. Moreover, there was a negative relationship between interindividual differences in initial Task and Bond scale scores and slope of PTSD symptoms over the course of therapy. By contrast, within-person variations in PTSD symptoms did not predict subsequent alliance components. The present results suggest the importance of agreement about therapy tasks during the process of IE or IR within prolonged exposure for PTSD patients, particularly in IE.