Idiopathic chronic pancreatitis (ICP) is the second most common subtype of CP. In 1994, researchers reported the bimodal age at onset of ICP symptoms: early-onset ICP (EO-ICP; median age, 19.2 years) and late-onset ICP (LO-ICP; median age, 56.2 years). Ages of onset and clinical features of ICP differed from those of alcohol-related CP (ACP). However, variants in PRSS1 had not yet been associated with ICP. We reexamined ages of onset of ICP in a large, North American cohort of patients, and investigated the effects of genetic factors and alcohol use in patients with EO-ICP, LO-ICP, or ACP.