Constipation (also known as costiveness or dyschezia) refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation. Severe constipation includes obstipation (failure to pass stools or gas) and fecal impaction, which can progress to bowel obstruction and become life-threatening. Constipation is a symptom with many causes. These causes are of two types: obstructed defecation and colonic slow transit (or hypomobility). About 50% of patients evaluated for constipation at tertiary referral hospitals have obstructed defecation. This type of constipation has mechanical and functional causes. Causes of colonic slow transit constipation include diet, hormonal disorders such as hypothyroidism, side effects of medications, and rarely heavy metal toxicity. Because constipation is a symptom, not a disease, effective treatment of constipation may require first determining the cause. Treatments include changes in dietary habits, laxatives, enemas, biofeedback, and in particular situations surgery may be required. Constipation is common; in the general population incidence of constipation varies from 2 to 30%. In the United States expenditures on medications for constipation are greater than $250 million per year.