IBS affects between 25 and 45 million people in the United States. About 2 in 3 IBS sufferers are female. About 1 in 3 IBS sufferers are male. Based on a survey taken by the Functional Bowel Disorder Severity Index (IFFGD), a considerable proportion – 35% to 40% – of people who register IBS in the community are male. About 60% to 65% of individuals who report IBS are female.