Neurotransmitters might participate in the development of diverticular disease. We measured fasting and postprandial serotonin levels in colonic diverticulosis patients and healthy volunteers. We demonstrated significantly lower maximal concentrations of serotonin in patients than the controls (respectively 109.8±61.4 and 251.3±44.1 ng/ml, p<0.001) as well as lower serotonin minimal values (respectively 38.4±21.8 and 124.6±41.4 ng/ml, p<0.001) and areas under time-course curves (respectively 288.8±139.8 and 739±167.4 ng/ml, p<0.001); significant difference between alternating pattern and normal bowel habit concerning fasting serotonin level, the hormone response to test meal (p=0.041) as well as minimal serotonin level (p=0.044). Bowel habit was also related to peak serotonin values following a test meal with 38.5 ng/ml in constipation, 139.5 ng/ml in diarrhea, 122.4 ng/ml in alternating pattern and 249 ng/ml in subjects with normal bowel habit (p=0.040) as well as AUC with 120.8 ng/ml in constipation, 416 ng/ml in diarrhea, 298 ng/ml in alternating pattern and 684 ng/ml in subjects with normal bowel habit (p=0.043). We demonstrated substantial differences in fasting serum serotonin levels as well as the hormone response to a test meal between colonic diverticulosis patients and healthy individuals, which seemed to be associated with abnormal bowel habits rather than presence of diverticula.