Human herpesvirus type 6 (HHV-6) has been well described as an agent of meningoencephalitis in post-haematopoietic stem cell transplantation patients, but is a rare cause of meningoencephalitis in immunocompetent adults. We report an immunocompetent adult with HHV-6-associated meningoencephalitis. The patient was an elderly diabetic man who presented with fever and confusion, with cerebrospinal fluid (CSF) pleocytosis. HHV-6 DNA was amplified from CSF by polymerase chain reaction. In our review of the medical literature we examine clinical presentations, laboratory findings, neuroimaging studies, treatments and clinical outcomes in immunocompetent patients with HHV-6 meningoencephalitis.