BackgroundThe aetiologies of acute pancreatitis in young adult patients are poorly known. AimsTo prospectively evaluate the causes of acute pancreatitis in patients aged less than 35 years. MethodsOverall, 309 consecutive patients admitted to our centre for acute pancreatitis received first-line investigations, including medical history, standard laboratory tests, abdominal ultrasound and computed tomography. If no aetiology was found, second-line investigations were performed, including endoscopic ultrasound, magnetic-resonance cholangiopancreatography and genetic testing in cases of idiopathic pancreatitis. ResultsOverall, 66 patients aged between 16 and 35 years were included. After first-line investigations, 49% of cases of acute pancreatitis remained idiopathic. Second-line investigations reduced this rate to 21%. The frequency of aetiologies for acute pancreatitis significantly differed in adults aged ≤35 compared to those aged >35 years: biliary aetiology was less frequent (23% versus 43%, p=0.003) as well as alcohol-related (8% versus 24%, p=0.01); drug-induced was more common (16% versus 4%, p=0.0007), as well as cannabis-related (13% versus 1%, p<0.0001), or genetic (10% versus 1.5%, p=0.003). ConclusionsThe aetiologies of acute pancreatitis significantly differed in adults aged less than 35 years when compared to older patients. Thus, use of medications, exposure to cannabis, and genetic mutations should be actively sought in these patients.