OBJECTIVE: To determine frequency, anatomic site, and host factors associated with asymptomatic shedding of herpes simplex virus after initial episodes of genital herpes. DESIGN: Cohort study with follow-up for a median of 63 weeks. SETTING: Referral clinic. PATIENTS: Women (306) with first episode of herpes; 43 had primary herpes simplex virus type 1, and 227 and 36 had primary and nonprimary herpes simplex virus type 2, respectively. MEASUREMENTS: Cultures were obtained for herpes simplex virus every 4 to 6 weeks at times in which genital lesions and symptoms were not present. MAIN RESULTS: Asymptomatic shedding was detected among 11.9%, 18.3%, and 22.9% of women with primary herpes simplex virus type 1, primary HSV type 2, and nonprimary HSV type 2, respectively. Among patients with type 2 infection, previous type 1 antibody was associated with a lower rate of asymptomatic vulvar shedding. Asymptomatic cervical shedding was 3 times more frequent during the first three months after resolution of primary type 2 disease than during later time periods. In contrast, the rate of symptomatic recurrent herpes did not change over time. CONCLUSIONS: Asymptomatic genital herpes simplex type 2 is more common than type 1. Asymptomatic genital shedding occurs more often during the first 3 months after acquisition of primary type 2 disease than during later periods. Patients with HSV type 2 should be advised of this high early rate of asymptomatic shedding and of potential transmission to sexual partners.