Context.-Intraductal carcinoma of the prostate (IDC-P) is a distinct clinicopathologic entity, characterized by an expansile proliferation of secretory cells within prostatic ducts and acini that demonstrate marked architectural and cytologic atypia. Intraductal carcinoma of the prostate is strongly associated with high-grade and high-volume, invasive prostate cancer and a poorer prognosis than cases without IDC-P. Objective.-To review the historic perspectives, pathologic and genetic features, diagnostic criteria and differential diagnoses, and the clinical significance of IDC-P. Data Sources.-Relevant studies indexed in PubMed. Conclusions.-It is critical to recognize IDC-P, especially in prostate biopsies in which the clinical implications of IDC-P are greatest. Morphologic criteria have been proposed to distinguish IDC-P from several other lesions with similar histologic appearance such as high-grade prostatic intraepithelial neoplasia, invasive cribriform prostate cancer, and urothelial carcinoma involving the prostate. Intraductal carcinoma of the prostate is an uncommon finding in prostate biopsies, and it is even rarer as an isolated finding without concomitant prostate cancer in biopsies. However, patients with isolated IDC-P in biopsies are recommended for either definitive treatment or immediate repeat biopsy.