Between the time that two large, national surveys were conducted, the Second National Health and Nutrition Examination Survey (1976-1980) and the Third National Health and Nutrition Examination Survey (1988-1994), prevalence of herpes simplex virus type 2 (HSV-2) infection in the United States increased by 30%. From these survey data, the authors estimated the incidence of HSV-2 infection in the civilian, noninstitutionalized population aged > or = 12 years by means of a mathematical model that allowed overall incidence to increase linearly with time but required the shape of the age-specific incidence curve to remain constant. From 1970 to 1985, annual incidence of HSV-2 infection in HSV-2-seronegative persons increased by 82%, from 4.6 per 1,000 (95% confidence interval: 4.2, 5.0) to 8.4 per 1,000 (95% confidence interval: 7.7, 9.1). Incidence in 1985 was higher in women than in men (9.9 vs. 6.9 per 1,000), higher in Blacks than in Whites (20.4 vs. 6.3 per 1,000), and highest in the group aged 20-29 years (14.6 and 22.5 per 1,000 in men and women, respectively). Thus, by 1985, approximately 1,640,000+/-150,000 persons (730,000 men and 910,000 women) were being infected annually with HSV-2.