Acute and chronic pancreatitis are most frequently caused by a high consumption of alcohol and tobacco but often the aetiology is unknown. The diseases have a high risk of complications, but the long-term prognosis and the natural course of the diseases are only sparsely described. The aims of the study were to investigate the long-term prognosis of acute pancreatitis (AP) and chronic pancreatitis (CP), the risk of progression to CP, and the natural course of progressive acute pancreatitis. Hereby, describe the prognostic factors associated with mortality and the causes of death in these patients. The study was based on the large prospective cohort study - Copenhagen Pancreatitis Study - of patients in the Copenhagen Municipality admitted with either AP or CP fulfilling specific diagnostic criteria and enrolled in the study during 1977 to 1982 and in 2008 followed up by linkage to the Danish registries. Factors associated with mortality in AP patients were high age, alcohol and diabetes, whereas female gender, employment, and co-living were associated with better survival. Level of S-amylase had no impact on the mortality. AP can progress to CP not only from alcoholic but also from idiopathic AP within a mean interval of 3.5 years. The mortality of progressive AP was 5-7 times higher compared with the background population. Patients with definite CP had a 4-fold higher mortality than the background population and patients with a suspicion of CP had twice the mortality compared with the background population. Unlike alcohol and smoking, both non-employment and being underweight had a significant impact on survival in CP patients. In the future, when diagnosing AP, we suggest focusing more on the elimination of differential diagnosis than on the level of S-amylase. The high mortality in progressive AP indicates that patients with risk factors for CP should be followed up. As both AP and CP are multifaceted, treatment for smoking dependency, alcohol dependency, and social and nutritional support is encouraged. More knowledge could be provided by interventional treatment of these four focus areas in patients with AP and CP.