Objective: To systematically evaluate the ETS-related gene (ERG) alterations in the multifocal tumor context using whole-mount prostatectomy specimens from African and Caucasian American patients matched for age, pathologic grade and stage. Oncogenic activation of the ERG is the most common early genomic alteration in patients with prostate cancer (CaP) in Western countries. However, ERG alterations have not been systematically examined in African American patients with a known greater risk of CaP incidence and mortality. Methods: ERG oncoprotein expression was analyzed in 91 Caucasian and 91 African American patients with CaP, who were matched for age, Gleason score, and pathologic stage. A unique aspect of the present study was the evaluation of ERG in whole-mount prostatectomy sections, minimizing sampling bias and allowing the careful assessment of the ERG in the multifocal tumor context of CaP. Results: The frequency of ERG-positive prostate tumors was significantly greater among Caucasian Americans than among African Americans when assessed in all tumor foci (41.9% vs 23.9%, P <.0001). A markedly greater frequency of ERG oncoprotein expression was noted between the index tumors of the Caucasian Americans (63.3%) and those of the African Americans (28.6%). Also, in the African American patients, the higher grade index tumors were predominantly ERG negative. Conclusion: ERG typing of CaP established a major difference between the index tumors of Caucasian and African American patients. ERG-negative index tumors might indicate a less favorable outcome for African American patients. The results of the present study underscore that typing of CaP for the ERG could enhance our understanding of the biologic differences between the examined ethnic groups.