We report the first case of human herpesvirus-6 (HHV-6) associated exanthema in a patient with acute lymphocytic leukaemia (ALL). We analysed DNA extracted from an exanthematous lesion using the polymerase chain reaction (PCR). DNA was positive for HHV-6 but negative for herpes simplex virus, varicella zoster virus, and cytomegalovirus. Immunohistochemical staining of the skin with monoclonal antibody against (HHV-6 confirmed the infection. The possibility of HHV-6 infection should be considered when an atypical skin rash is seen in patients with ALL.