High immune cell infiltration is generally associated with better survival in colorectal cancer (CRC). Recently, a prognostic score called CD8(IE)-FOXP3(IS), which integrates the densities of tumor intraepithelial CD8(+) and intrastromal FOXP3(+) cells, was introduced using multiplex immunofluorescence. In this study, we developed a triple chromogenic immunohistochemistry assay to evaluate the CD8(IE)-FOXP3(IS) score and assessed its prognostic value in comparison with the CD3-CD8 T-cell density score (based on the principles of the Immunoscore) and conventional prognostic parameters. Multiplex immunohistochemistry combined with machine learning-assisted image analysis was used to quantify CD8(IE) and FOXP3(IS) densities in 2 independent cohorts comprising 1724 CRC patients. Multivariable Cox regression models were used to evaluate the prognostic value of the CD8(IE)-FOXP3(IS) score. We found that a low CD8(IE)-FOXP3(IS) score was associated with higher disease stage, more frequent lymphovascular invasion, and mismatch repair proficient status. In addition, a low CD8(IE)-FOXP3(IS) score was associated with higher CRC-specific mortality independent of the CD3-CD8 T-cell density score and other tumor and patient characteristics (cohort 1: hazard ratio [HR] for low vs high CD8(IE)-FOXP3(IS) score, 3.08; 95% CI, 1.54-6.15; P(trend) = 6.0E-4; cohort 2: HR, 4.30; 95% CI, 2.58-7.17; P(trend) = 3.2E-9). These findings indicate that triple chromogenic immunohistochemistry combined with digital pathology is an applicable method for quantifying tumor intraepithelial CD8(+) and stromal FOXP3(+) cell densities, allowing for the determination of the CD8(IE)-FOXP3(IS) score. The CD8(IE)-FOXP3(IS) score shows a strong prognostic value, which appears superior to overall CD3(+) and CD8(+) T-cell density measurement.