Can adults with genital herpes develop encephalitis?

Possible: This is unlikely, and would be in high risk patients (i.e. Those that are immunosuppressed).

Unlikely: There is a definite association between herpes simplex type 2 and recurrent (mollaret's) meningitis, but encephalitis would be very unusual in an immune competent host. On the other hand, genital herpes can be due to type 1, and that can certainly, but uncommonly, produce meningitis, encephalitis or meningoencephalitis unpredictably.