Elastosis of the prostate may be seen on needle biopsy and radical prostatectomy specimens, but its significance is unknown. Prostatic atrophy (or postatrophic hyperplasia) is one of the most frequent mimics of prostatic adenocarcinoma. To observe the frequent occurrence of elastosis of the prostate stroma in areas of postatrophic hyperplasia. A step-section method was used to cut the posterior lobe (or peripheral zone) in coronal planes at intervals of 0.3 to 0.5 cm in 100 consecutive autopsy specimens of men older than 40 years. Elastosis was detected because of a basophilic tinge of the stroma on hematoxylin-eosin stain and confirmed using elastic fiber stains. Presence of elastosis correlated with the following variables: age, prostatic atrophy (simple, hyperplastic, or sclerotic), local arteriosclerosis, histologic carcinoma, high-grade prostatic intraepithelial neoplasia, benign or malignant nephrosclerosis, generalized atherosclerosis, nodular prostatic hyperplasia, and acute inflammation. For statistics, a stepwise linear regression method adjusted for age was used. Elastosis was found in 65 of the prostates examined and was significantly more frequent with increasing age (P <.001), prostatic atrophy (P <.001), and local arteriosclerosis (P <.02). There was no significant relation to histologic carcinoma, high-grade prostatic intraepithelial neoplasia, benign or malignant nephrosclerosis, generalized atherosclerosis, nodular prostatic hyperplasia, and acute inflammation. The correlation with local arteriosclerosis favors a possible role of ischemia to its etiopathogenesis. The absence of correlation to neoplastic and preneoplastic lesions and the striking spatial relationship of elastosis to prostatic atrophy (or postatrophic hyperplasia) add a new microscopic feature for the diagnosis of this latter lesion, helping in the differential diagnosis with prostate adenocarcinoma.1241306-9