Gonococcal infections are frequently recurrent and are sustained in human populations by core groups, composed of very sexually active individuals, that have a high incidence and prevalence of infection. Recent advances in typing of gonococci have documented extreme strain heterogeneity, and epidemiologic studies have shown that gonococci vary widely between different geographic regions, within different population groups in a region, and within a given human population over time. The hypothesis of strain-specific immunity to gonococcal infection explains the diversity, dynamics, and recidivism so well-recognized for this organism. If true, this hypothesis will have some bearing on vaccine development and will suggest alternate strategies for disease control.