The mouse model of genital herpes relies on medoxyprogesterone treatment of female mice to render the vaginal lumen susceptible to inoculation with herpes simplex virus 2 (HSV-2). In the present study, we report that mice deficient in the A1 chain of the type I interferon receptor (CD118 ؊/؊ ) are susceptible to HSV-2 in the absence of medroxyprogesterone preconditioning. In the absence of hormone pretreatment, 2,000 PFU of a clinical isolate of HSV-2 was sufficient to establish a productive infection in the vagina of 75% ؎ 17% and in the spinal cord of 71% ؎ 14% of CD118 ؊/؊ mice, whereas the same dose of HSV-2 replicated to detectable levels in only 13% ؎ 13% of vaginal samples and 0% of spinal cord samples from wild-type mice, as determined at day 5 postinfection. The susceptibility to HSV-2 infection in the CD118 ؊/؊ mice was associated with a significant reduction in the infiltration of HSV-specific cytotoxic T lymphocytes into the vaginal tissue, the local production of gamma interferon (IFN-␥), and the expression of T cell-recruiting chemokines CCL5, CXCL9, and CXCL10. Collectively, the results underscore the significant contribution of type I IFNs in resistance to genital HSV-2 infection.