The acute clinical events surrounding the acquisition of human immunodeficiency virus (HIV) have not been well characterized.

To further define the clinical and epidemiologic presentation of primary HIV infection.

Descriptive cohort study.

University research clinic.

46 adults (43 men and 3 women) with primary HIV infection who enrolled in the study a median of 51 days after HIV seroconversion.

Documentation of recent HIV seroconversion. Standardized collection of demographic characteristics and sexual contact history, results of tests for HIV RNA, HIV culture, and T-cell subsets.

41 of 46 patients (89%) developed an acute retroviral syndrome. Primary HIV infection was infrequently diagnosed at the initial medical encounter, even in persons enrolled in routine HIV screening programs. Median numbers of sexual partners 6 months and 1 month before acquisition of HIV were three and one, respectively; 21 patients (46%) reported having had only one partner in the month before seroconversion. Of the 12 patients who could identify the precise date of and activity leading to seroconversion, 4 reported having only oral-genital contact.

Primary HIV infection causes a recognizable clinical syndrome that is often underdiagnosed, even in persons enrolled in a program of routine surveillance for HIV infection. Frequency of sexual contact and overall numbers of sexual partners in this group of homosexual men who acquired HIV were markedly lower than those seen a decade ago. Acquisition of HIV does occur, even in persons with relatively few sexual partners. Increased attention to oral-genital contact as a means of acquiring HIV appears to be warranted.