The epidemiology of Herpesvirus sylvilagus infection in wild cottontail rabbits was studied in a defined, natural cottontail population over a period of 13 months. Spread of this virus showed significant correlation with seasonal variation as well as with the sex and age of the host. The highest rate of infection occurred during the winter and spring seasons with males over the age of 4 months sustaining a significantly greater percentage of infections than younger males or females of all age groups.