Aggressive screening and prostate needle biopsy protocols have been successful in early detection of low-volume posterior tumors. Consequently, we have observed an increased incidence of anterior-predominant prostate cancers. However, the zones of origin, patterns of spread, and patterns of extraprostatic extension of this group of tumors have not been well studied. Of 1312 radical prostatectomies performed at our institution over a span of 4.5 years, 197 had predominant (largest) tumors anterior to the urethra in whole-mounted radical prostatectomy specimens. Detailed histopathologic analysis of this cohort was undertaken emphasizing the variability in anterior prostatic anatomy from apex through base to determine zone of origin and pathologic staging. Using this approach, 97/197 (49.2%) anterior-predominant tumors (ATs) were assigned to the anterior peripheral zone (APZ), 70 (35.5%) to the transition zone (TZ), 16 (8.1%) were of indeterminate zone, and 14 (7.1%) were of both zones. Comparing APZ and TZ tumors, there were no significant differences in Gleason scores, incidence of extraprostatic extension, overall surgical margin positivity rate, or laterality. Involvement of the anterior fibromuscular stroma was significantly more likely in tumors of TZ origin (P< or =0.01), yet was observed in 50.5% of APZ tumors. Conversely, APZ tumors were more commonly localized within the apical one third of the prostate. Most of the prostates (91.4%) also showed additional PZ tumors, which were occasionally stage determining (7/197; 3.9%). In conclusion, ATs of APZ origin are more prevalent than those arising from the TZ. Contrary to previous reports comparing TZ tumors to all PZ tumors, ATs of both zones exhibit similar grading and staging parameters in this series. Given these similarities, long-term clinical outcomes and future molecular analyses will be necessary to assess whether true differences in biology and behavior exist between tumors of TZ and APZ origin.