Irritable bowel syndrome (IBS) is a common chronic gastrointestinal disorder that considerably reduces quality of life and is an economic burden on society. The pathogenesis of IBS is unknown. However, intestinal low‑grade inflammation has been proposed as one of the factors contributing to the development of IBS. The present study aimed to examine the possible occurrence of low‑grade inflammation in the rectum of patients with sporadic IBS. In total, 50 patients (42 females and 8 males with an average age of 34 years) with sporadic IBS fulfilling the Rome III Criteria were recruited for this study. Of these, 30 patients had IBS with diarrhoea as the predominant symptom (IBS‑D) and 20 patients had IBS with constipation as the predominant symptom (IBS‑C). A total of 27 control subjects (19 females and 8 males with an average age of 53 years) were included. The patients and controls underwent colonoscopy with rectal biopsies. The biopsies were immunostained for total leucocytes, lymphocytes, monocytes, macrophages and mast cells. The mucosal density of these cells was quantified by computer image analysis. The number of intraepithelial leucocytes and the density of the leucocytes in the lamina propria of the IBS patients did not differ from that of the controls. Similarly, there was no difference in the cell density of the mast cells in the lamina propria between the patients and the controls. The numbers of mucosal lymphocytes, macrophages and monocytes were low in the patients and the controls. These findings oppose low‑grade inflammation as a pathogenic factor in sporadic IBS. Low‑grade inflammation may, however, play an important role in the pathogenesis of a subset of IBS, namely post‑infectious IBS (PI‑IBS).