Irritable bowel syndrome (IBS) is characterized by abdominal pain and alteration of bowel habits. Manning et al. have reported that certain symptoms distinguished IBS from organic gastrointestinal disease (OGD); these were pain relieved by defecation, looser or more frequent stools at the onset of pain, abdominal distention, mucus, and a feeling of incomplete evacuation. Another simple scoring system for discriminating IBS from OGD that incorporated historical data, physical examination findings, and basic investigations was first devised by Kruis et al. In differential diagnosis of IBS from OGD, to evaluate the reliability of Manning's criteria and Kruis scoring system when used apart or combined; we studied 347 out-patients who completed a bowel disease questionnaire which objectively measured Manning's criteria and scoring system of Kruis. The group included 165 patients with IBS and 182 patients with OGD. The Manning's criteria discriminated IBS from OGD with a sensitivity of 90% and a specificity of 87% if three or more items were regarded as positive. Also the Kruis scoring system discriminated IBS from OGD with a sensitivity of 81% and a specificity of 91%. When used together, these systems discriminated IBS from OGD with a sensitivity of 80% and a specificity of 97%. Manning's criteria and Kruis scoring system had a strong correlation when compared in IBS, but not in OGD.