Résumé : Objectives. There is little objective information on what is designated as being the prostate capsule. We have quantified objectively with computerized image analysis the percentage of smooth muscle fibers (SMFs) surrounding the surgical specimens of radical prostatectomies. Methods. Ten radical prostatectomy specimens were used. Six different parts from each prostate lobe were analyzed. Thirty different fields were examined from each tissue section. For tissue sections, different stains were used: hematoxylin and eosin, Masson's trichrome, and immunohistochemical staining with antiactin for the SMFs. Results. The mean thickness of the prostate capsule was 0.5 to 2 mm. The mean percentages of SMFs in the different regions of the prostate capsule was 30.6%. No difference was noted between the percentage of SMFs in the prostatic capsule compared with that in the prostate parenchyma itself (30.7%). Conclusions. This study provides objective evidence to demonstrate that the prostate does not have a true capsule. This capsule represents a fibromuscular band that probably should be considered as the extension of the internal parenchyma.