Liver involvement is an unusual manifestation of Mycoplasma pneumoniae infection. Cases of cholestatic hepatitis without pulmonary involvement have been described in children with M. pneumoniae infection but only two cases of cytolytic hepatitis have been reported in adults. We report here the case of an 18-year-old woman who presented with febrile epigastric pain of short duration associated with an elevation of gamma-glutamyl transpeptidase and alkaline phosphatase levels and with a mononuclear syndrome. Serological tests for M. pneumoniae were positive for IgG and IgM. Clinical symptoms and blood test perturbations completely resolved after treatment with macrolide.