Constipation is a symptom caused by several different pathogenetic mechanisms; it may be secondary to other diseases or be in itself a disease. All patients should perform investigations deemed to exclude or identify known causes of constipation and, in the presence of megarectum, anorectal manometry to detect ultrashort Hirschsprung's disease. In idiopathic constipation, diagnostic work up should attempt to identify alterations of defecation, with defecography, and of colonic propulsion, with gastrointestinal transit time measurement. Evaluation of large bowel segmental transit time, using radiopaque corpuscolate markers, may discriminate patients according to different modalities of transit. Based on a correct diagnostic evaluation the therapeutical approach can be finalized to well defined subgroups of patients. The treatment comprises several types of therapy which may be used alone or in association in the individual patient: bowel training, high residue diets, physiotherapy, bio-feedback, pharmacological therapy, psychiatric therapy, surgery.