While post-vaccinal encephalitis in children is unfortunately well known, its occurrence in adults is rather exceptional. The calendar of a poly vaccination situated so close to each other, most probably account for such an evolution. The case reported concerns a man of 27 years who presented 10 days after a polyvaccination (7 vaccines in 2 months) altered consciousness, epileptic fits, right hemiplegia, vegetative dysfunctions and meningeal status. Evolutionary clinical course led to death in 21 days. Neuropathological findings showed lymphocytic infiltrates in the cortex and basal ganglia, congestive aspect with petechial areas in the white matter and inflammatory meningeal infiltrates. All viral investigations both in the blood, brain and cerebrospinal fluid remained negative. Post-vaccinal encephalitis is reviewed. Vaccination cannot be condemned, but in case of polyvaccination lapse of time in between vaccines should be longer so as to prevent such exceptional evolution and fatal course.