An epidemiologic survey of idiopathic intracranial hypertension (IIH) in Benghazi, Libya, over a period from September 1982 through August 1989 ascertained 81 patients. The group was comprised of 76 females and 5 males. Ages ranged from 8 to 55 years; the mean +/- S.D. was 28.6 +/- 7.9 for women and 21.0 +/- 14.5 for men. The average crude annual incidence rates for IIH per 100,000 persons were 2.2 for the total and 4.3 for females for all ages (3.2 for the total and 5.9 for the females when adjusted to the 1980 United States population). In females aged 15-44 years, IIH occurred at a rate of 12.0 per 100,000 per year; for those defined as obese, the rate rose to 21.4. Moderate to severe visual loss occurred as a sequelae in 20% of our patients. The extent of visual loss did not correlate with age at diagnosis, duration of symptoms, degree of obesity, use of oral contraceptive pills, cerebrospinal fluid (CSF) opening pressure, steroid treatment, or recurrence. We found no correlation between CSF protein and opening pressure. We conducted a case-control study on 40 consecutive female incident IIH patients and 80 age-matched female control subjects. Obesity and recent weight gain occurred more frequently in patients. More patients were married and more had irregular menses. The incidence rate for IIH described in our study is three to four times higher than that reported from the United States.