In humans chronic obstructive pancreatitis (COP) is thought to be a disease devoid of ductal stones. The aim of this study was to verify the presence and frequency of calcifications in patients with COP and compare them with those found in patients with chronic calcifying/calcific pancreatitis (CCP). We conducted a retrospective ERCP investigation in 115 patients with documented chronic pancreatitis. Only 75 could be safely classified as COP or CCP. Fifty-three patients (M:F ratio, 5.6:1; mean age, 36.1 +/- 12.2 years) had CCP, 46 of whom (86.8%) with calcifications. Twenty-two patients (M:F ratio, 3.4:1; mean age, 45.3 +/- 16.2 years; p < 0.05 vs. CCP) presented COP at endoscopic retrograde cholangiopancreatography, 8 (36.4%) with ductal calcifications (p < 0.0001 vs. CCP). COP was secondary to acute pancreatitis in nine cases, to odditis in 11 cases, and to malignant tumor and hypertrophy of Oddi's sphincter, respectively, in the other two cases. The two patient groups showed no significant differences in drinking and smoking habits, number of painful relapses, disease duration, and incidence of diabetes, gallstones, and need for surgery. In conclusion, formation of ductal stones is by no means rare in COP and should be classified as a form of lithiasic pancreatitis. Early restoration of pancreatic outflow by removing the obstruction, or by shunt-type operations and abstinence from drinking and smoking, should resolve this type of disease.