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Cases of colo-ileal carcinoma (CIC), defined as intestinal carcinoma involving the right-sided colon and the ileum, are rarely encountered. The aim of this study was to elucidate the clinicopathological characteristics, which have been poorly understood, in such cases. A total of 16 CICs were examined histologically and immunohistochemically. Microsatellite instability-related histology was also evaluated according to previously published models, such as MsPath and PREDICT. CICs included 14 adenocarcinomas and 2 mucinous adenocarcinomas. The CICs showed focal or diffuse cytokeratin 20 expression and 7 CICs showed focal cytokeratin 7 co-expression. MsPath and PREDICT scores ranged from 1.6 to 6.6 (mean, 3.14) and from 1.6 to 7.8 (mean, 3.86), respectively. Three CICs showed loss of MLH1 immunoreactivity. Prominent neutrophilia and cancerous lymphangiosis in Peyer's patches (CLPP) were found in 8 cases (50%) and in 3 cases (18.8%), respectively. Neither variable was associated with parameters such as gender, tumor size or poor prognosis. However, the PREDICT score in prominently neutrophilic CICs was significantly higher than that in CICs with non-prominent neutrophilia (P=0.004). Patients with CLPP-positive CICs were significantly younger than those with CLPP-negative CICs (P=0.031). This study showed that almost all CICs originate from the right-sided colon with possible high levels of microsatellite instability. Prominent neutrophilia may be an additional histological indicator for microsatellite instability. Prognosis-independent CLPP occasionally occurs in younger patients with CICs.