We report 7 children with recent M. pneumoniae infection and severe GBS that presented to two European medical centers from 1992-2012. Severe GBS was defined as the occurrence of respiratory failure, central nervous system (CNS) involvement, or death. Five children had GBS, one Bickerstaff brain stem encephalitis (BBE), and one acute-onset chronic inflammatory demyelinating polyneuropathy (A-CIDP). The 5 patients with severe GBS were derived from an original cohort of 66 children with GBS. In this cohort, 17 children (26%) had a severe form of GBS and 47% of patients with M. pneumoniae infection presented with severe GBS. Of the 7 patients in this case series, 5 were mechanically ventilated and 4 had CNS involvement (2 were comatose). Most patients presented with nonspecific clinical symptoms (nuchal rigidity and ataxia) and showed a rapidly progressive disease course (71%). Antibodies against M. pneumoniae were detected in all patients and were found to be intrathecally synthesized in 2 cases (GBS and BBE), which proves intrathecal infection. One patient died and only 2 patients recovered completely. These cases illustrate that M. pneumoniae infection in children can be followed by severe and complicated forms of GBS. Nonspecific clinical features of GBS in such patients may predispose a potentially life-threatening delay in diagnosis.