On average, IIH occurs in about one per 100,000 people, and can occur in children and adults. The median age at diagnosis is 30. IIH occurs predominantly in women, especially in the ages 20 to 45, who are four to eight times more likely than men to be affected. Overweight and obesity strongly predispose a person to IIH: women who are more than ten percent over their ideal body weight are thirteen times more likely to develop IIH, and this figure goes up to nineteen times in women who are more than twenty percent over their ideal body weight. In men this relationship also exists, but the increase is only five-fold in those over 20 percent above their ideal body weight.