The causes of acute pancreatitis are well documented and usually are divided into alcohol-induced, gallstone, miscellaneous, and idiopathic when no immediate cause is found. Clinically, the cause is either immediately discernable from the history and a few standard investigations, less obvious and requiring more detailed studies, or obscure and even speculative. The physician can whittle away at the idiopathic group by increasingly recognizing causes such as biliary sludge or microlithiasis, sphincter of Oddi dysfunction, hereditary pancreatitis, cystic fibrosis, or autoimmune causes. The prevalence of these and other rare conditions is the focus of intense research. Whether these increasingly recognized causes will significantly alter the current incidence of 10% to 30% of cases classified as idiopathic pancreatitis, only time will tell.