The renin-angiotensin system (RAS) has been implicated in the pathogenesis of acute and chronic pancreatitis. Angiotensin-converting enzyme (ACE) is the key enzyme which activates RAS. The ACE intron 16 insertion/ deletion (I/D) polymorphism is associated with ACE activity and is considered to be a risk factor for several inflammatory processes. We investigated this polymorphism in 68 patients with acute pancreatitis (AP) and 157 healthy Turk­ish control subjects. Patients were evaluated with ultrasonography, abdominal tomography and labo­ratory markers and grouped by status for diabetes mellitus (DM), hypertension (HT), and both these diseases and by etiology. Genotyping of the I/D polymorphism was performed by polymerase chain reaction (PCR). The DD genotype was more preva­lent in healthy controls, however, genotype II was significantly more frequent in AP patients (p <0.05). In severe AP patients, the genotype II frequency was significantly higher than in controls (p <0.05). Acute pancreatitis patients with both DM and HT had lower frequencies of genotype DD and of the D allele, and higher frequencies of genotype II and of the I allele than patients with either DM or HT