Activating mutation of the Kras oncogene is the most frequent and perhaps the earliest genetic alteration associated with pancreatic cancer. To examine the link between mutant Kras and exocrine pancreatic cancer, we generated transgenic mice carrying an elastase-mutant Kras transgene, which targets expression to pancreatic acinar cells. Most elastase-Kras founder mice displayed perinatal pancreatic acinar cell hyperplasia and dysplasia. However, adult mice in two surviving lineages displayed preinvasive pancreatic neoplastic lesions with ductal morphology, thereby providing a unique mouse model in which lesion histotype and initiating genetic alteration overlap with the human disease. Our findings suggest that Kras mutation is associated with development of early stage duct-like lesions in pancreas, but that additional alterations must accompany progression to malignancy.