Psychotherapy is an efficacious and long used type of care. However, information available in specialized literature shows that this area has been little studied. The objective of this study is to determine the prevalence of use of outpatient psychotherapy by adult population, their related factors, and funding sources through systematic review, including qualitative and quantitative analyses of original articles with cross-sectional design and population-based sampling. Between January 1970 and December 2007, 3 databases were searched. A total of 2240 articles were identified, and 6 studies fulfilled the inclusion criteria. These studies investigated the prevalence of use of outpatient psychotherapy either in the moment or for 12 months or throughout life. Some of them investigated sociodemographic and health characteristics of users, costs, and treatment-funding sources. Studies' restricted number and different characteristics did not enable a meta-analysis. Six studies on the prevalence of use of outpatient psychotherapy were identified, thus revealing lack of data on this issue.