Two patients, men aged 39 and 52 years, are described with a mononucleosis-like syndrome, due to a primary HIV infection. Both patient developed dermatological manifestations. One patient presented with an encephalitis with an inversed CD4/CD8 cell ratio in the cerebrospinal fluid. Primary HIV infection is often missed as a clinical diagnosis. The possible preservation of a strong cellular immune response against HIV itself in case of early start of treatment argues for an immediate intervention with a combination of antiretroviral drugs in this syndrome.