Cyclin D1 is an important regulator of the G1 phase of the cell cycle. In this study we examined the expression and localization of cyclin D1 in chronic pancreatitis (CP), a condition associated with fibrosis, acinar cell degeneration, and foci of duct cell proliferation. Northern blotting of total RNA from the normal pancreas and from the pancreas of patients with CP revealed the presence of a 4.4-kb cyclin D1 mRNA transcript in all samples. Densitometric analysis indicated that pancreatic cyclin D1 mRNA levels were 2.0-fold increased in CP compared to normal controls (p = 0.0046). In the normal pancreas, faint cyclin D1 immunoreactivity was present in the nuclei and cytoplasm of some ductal cells and islet cells. In contrast, in CP, moderate to strong cyclin D1 immunoreactivity was present in many ductal and islet cells, as well as in some acinar cells and fibroblasts. These findings raise the possibility that enhanced cyclin D1 expression may contribute to a hyperproliferative state in CP.