Progress feedback is an intervention aimed at enhancing patient outcomes in routine clinical practice. This study reports a comprehensive multilevel meta-analysis on the effectiveness of progress feedback in psychological treatments in curative care. The short- and long-term effects of feedback on symptom reduction were investigated using 58 (randomized and non-randomized) studies, analyzing 110 effect sizes in a total of 21,699 patients. Effects of feedback on dropout rate, percentage of deteriorated cases, and treatment duration were also examined. Moderation analyses were conducted for study and feedback characteristics. A small significant effect of progress feedback on symptom reduction (d = 0.15, 95% CI: [0.10, 0.20]) was found, compared to control groups. This was also true for not-on-track cases (d = 0.17, 95% CI: [0.11, 0.22]). In addition, feedback had a small favorable effect on dropout rates (OR = 1.19, 95% CI: [1.03, 1.38]). The moderation analyses identified several potentially interesting variables for further research, including feedback instrument, outcome instrument, type of feedback, feedback frequency, treatment intensity, and country in which the study was conducted. Future studies should report on these variables more consistently so that we can obtain a better understanding of when and why feedback improves outcomes.