This fourth series Fascicle in the American Registry of Pathology/Armed Forces Institute of Pathology Atlas of Tumor Pathology series discusses the practical pathologic diagnoses of tumors and tumor-like diseases of the prostate gland, seminal vesicles, penis, and scrotum. The authors follow the tradition of the preceding three Fascicles by emphasizing pathologic gross and light microscopic diagnostic features and differential diagnoses. They also discuss relevant clinical features, including concise sections on the clinical presenta tion and the clinical meaning of the pathologic diagnosis in terms of prognosis and treatment. The immunohistochemical and molecular pathologic studies that are of current value in diagnosis are clearly presented. The high quality images follow the rich tradition of the previous Fascicles to depict the spectrum of tumor morphology from cases mainly from the files of institutions such as The Johns Hopkins Hospital, Barnes-Jewish Hospital, and Instituto de Patología e Investigación. This Atlas will be of great value in the field of pathology of the prostate gland, seminal vesicles, penis, and scrotum for years to come.