High-grade prostatic intraepithelial neoplasia (PIN) is the only widely accepted precursor lesion for prostatic adenocarcinoma (PCa). However, the spread of established PCa within prostatic ducts may be indistinguishable morphologically from high-grade PIN. By convention, all cytologically malignant cellular proliferations within prostatic ducts have been lumped into a PIN category, although there have been recent attempts by McNeal to develop reproducible criteria to separate high-grade PIN from the spread of established PCa within prostatic ducts--intraductal carcinoma (IDCa). Using McNeal's criteria for IDCa, we studied whole-mount sections from 252 patients with pT3NO PCa for the presence of IDCa and correlated the presence or absence of IDCa with Gleason score, total tumor volume, surgical margin status, seminal vesicle involvement, and disease progression. Patients with IDCa had higher Gleason score and total tumor volume and were more likely to show seminal vesicle involvement and disease progression than those patients without IDCa. In addition, IDCa was of independent prognostic significance. Total tumor volume and surgical margin status had no independent prognostic significance in this data set.