This study examined rates of improvement in psychotherapy as a function of the number of sessions attended. The clients (N = 1,868; 73.1% female; 92.4% White; average age = 40), who were seen for a variety of problems in routine primary care mental health practices, attended 1 to 12 sessions, had planned endings, and completed the Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM) at the beginning and end of their treatment. The percentage of clients achieving reliable and clinically significant improvement (RCSI) on the CORE-OM did not increase with number of sessions attended. Among clients who began treatment above the CORE-OM clinical cutoff (n = 1,472), the RCSI rate ranged from 88% for clients who attended 1 session down to 62% for clients who attended 12 sessions (r =-0.91). Previously reported negatively accelerating aggregate curves may reflect progressive ending of treatment by clients who had achieved a good enough level of improvement.