Randomised controlled trials provide evidence for the efficacy of psychotherapeutic interventions. Short protocolled courses of cognitive-behaviour therapy (e.g., 10 to 15 sessions, the typical format in rct's) lead to a greater decrease of complaints than no treatment. These findings from clinical research have made health care policy makers and insurance companies argue for time-limited therapy. This paper argues that such conclusions are premature and based on a misunderstanding of findings from psychotherapy treatment outcome research. More specifically, the distinction between efficacy and clinical effectiveness is ill understood. Clinical effectiveness of psychotherapy refers to the effects of treatment in clinically meaningful terms (e.g., the number of recovered patients) when the treatment is applied in real life settings. Until now, data on the clinical effectiveness of efficacious treatments are scarce and more research is called for to investigate how much treatment is sufficient and for whom.