Increasing attention is devoted to the patient perspective in mental health services research. Consequently, patient satisfaction has taken a prominent role and is frequently applied as an indicator of treatment quality and even outcome. However, the suitability of patient satisfaction for assessing quality of mental health services is doubtful, and there is a lack of longitudinal data especially for outpatient psychotherapy. By using data of the TRANS-OP study, we examine the course of patient satisfaction in outpatient psychotherapy over time and its predictors such as symptom change and duration of treatment. Furthermore, the relation between treatment satisfaction ratings of patients and therapists will be scrutinized. This study was conducted by the Center for Psychotherapy Research in Stuttgart (now Heidelberg) in cooperation with the Deutsche Krankenversicherung. N = 714 participants who applied for reimbursement of outpatient psychotherapy were consecutively recruited and asked to provide data at five (therapists two) measurement points during a two-year period. In line with previous evidence, high rates of patient satisfaction have been found, and also therapists appraised favorably the quality of their treatments. Course of patient satisfaction was found to be markedly stable over time. While some variables related to initial patient satisfaction, its course could hardly be predicted. Treatment outcome and session number moderately affected satisfaction at treatment termination. Concordance between patients' and therapists' satisfaction ratings was poor. Implications of these findings for research and practice are discussed.