The recently introduced Freiburg index of patient satisfaction (FIPS) is a new questionnaire to assess treatment-related patient satisfaction after surgery and interventional procedures. The questionnaire had first been tested psychometrically in a mixed population of urology patients. The current study describes the results of an interdisciplinary validation. In addition, an English version is presented. The questionnaire was used in two cohorts of cardiology (n = 120) and surgical (n = 127) patients. The evaluation included a comprehensive methodological and statistical evaluation including validation in comparison to the ZUF-8 questionnaire. The psychometric evaluation showed good results. The analyzed samples showed no missing values or ceiling effects. Furthermore, a high reliability (Cronbach's alpha 0.82), unidimensionality, sufficient distribution of values and validity (high correlation to the ZUF-8, r = 0.65, p < 0.001) of the questionnaire could be confirmed. The FIPS constitutes an interdisciplinary validated questionnaire to evaluate treatment-related patient satisfaction which can be used to objectify and compare results from clinical studies and quality in patient care. Colleagues of English-speaking countries are invited to participate in the validation of the hereby presented English version.