Context The usefulness of stool calprotectin determination in diagnosis of inflammatory disease of the colon has been reported; information about its usefulness for patients with polyposis are scarce, however. Objective To evaluate the significance of stool calprotectin concentrations for patients affected by colonic polyposis. Patients Sixty-three consecutive patients (35 males, 28 females, mean age 60.3 years, range 39-78 years) were enrolled: 26 patients (41.3%) with polyps, 17 patients (27.0%) with asymptomatic diverticular disease, and 20 subjects (31.7%) with normal endoscopic appearance of the colon. Results Stool calprotectin concentrations were 17.4 ± 24.5 lg g -1 for patients with colonic polyposis, significantly higher than concentrations for patients with diverticulosis (7.1 ± 5.7 lg g -1 ; P = 0.026) or for patients with normal appearance of the colon (calprotectin 6.0 ± 5.8 lg g -1 ; P = 0.003). For patients with a single polyp, stool calprotectin concentrations were similar to those for patients with multiple polyps. Calprotectin fecal concentrations for patients with sessile polyps and those with flat polyps were not significantly different. Calprotectin concentrations were not significantly related to the size of the polyps. Conclusion Our data show that colonic polyposis may cause an increase in stool calprotectin values and that these colonic lesions should be suspected when elevated stool calprotectin concentrations are found.