Pancreatobiliary versus intestinal histologic type of differentiation is an independent prognostic factor in resected periampullary adenocarcinoma. To differentiate these two histologic type proactively before surgery, we tried to use whole-lesion histogram analysis of apparent diffusion coefficient (ADC) derived from diffusion-weighted imaging . Entropy was significantly lower in pancreatobiliary-type periampullary carcinoma and achieved the best diagnostic performance. ADC value was relatively lower in pancreatobiliary-type. No significant difference was shown between lymph node metastasis positive and negative group. So we hypothesized that ADC histogram parameters might help to differentiate these two histologic type without the influence of lymph nodal involvement.