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The immune microenvironment is a crucial component of colorectal carcinoma that has been well characterized, but much less is known about the immune microenvironment of colorectal carcinoma precursors. We hypothesized that T-cell infiltrates might differ across the colorectal neoplastic spectrum. We leveraged the prospective cohort incident-tumor biobank method, which provided formalin-fixed, paraffin-embedded tumor tissue specimens (N = 1,825) from 790 colorectal carcinoma precursors (including hyperplastic polyps, sessile serrated adenomas, traditional serrated adenomas, tubular adenomas, tubulovillous adenomas, and villous adenomas) and 1,035 colorectal carcinomas. We performed an in situ multispectral immunofluorescence assay for CD3, CD4, CD8, FOXP3 (negative, low, or high expression), PTPRC (CD45RO and CD45RA), MKI67 (Ki-67), and KRT (keratin) combined with supervised machine learning. CD3+CD4+ cells were more abundant than CD3+CD8+ cells in most precursors. In conventional adenomas, greater villous component correlated with fewer intraepithelial CD3+CD8+ cells. Serrated lesions, including hyperplastic polyps and sessile serrated lesions, exhibited higher densities of intraepithelial CD3+CD8+ cells compared with other precursors and carcinomas. Age strata of patients with precursors (including early-onset precursors) were not associated with differential T-cell infiltration patterns. Compared with invasive colorectal carcinoma, precursors generally showed higher densities of CD3+CD4+ cells and CD3+CD8+ cells with phenotypes of naive (CD45RA+CD45RO-), memory (CD45RA-CD45RO+), and regulatory (FOXP3+Low and FOXP3+High) in intraepithelial and lamina propria/stromal regions. In conclusion, T-cell infiltration patterns vary across different histopathologic types of the colorectal neoplastic spectrum from precursors to invasive carcinomas. Our findings shed light on how the tumor-immune microenvironment evolves during precursor development and progression to colorectal carcinoma.