This study comprised 62 outpatients with ulcerative colitis who underwent 64 colonoscopies. The disease activity was evaluated according to endoscopic and histological criteria. The results revealed a significant correlation between both the endoscopic as well as the histological gradings of disease activity and faecal calprotectin. The median faecal calprotectin levels in the control group (6 mg/l) and in the patients with no or low disease activity (11.5 mg/l) were significantly different (p < 0.0001). The median calprotectin level among patients with active disease was 68 mg/l which was significantly different from the latter group (p < 0.0001). Furthermore, we suggest that the degree of inflammation rather than the extent of the disease determined the faecal calprotectin levels. In conclusion, assessment of faecal calprotectin seems to be a marker of disease activity in patients with ulcerative colitis.