It has been suggested that a previous viral or bacterial pharyngitis may predispose to Lemierre's syndrome, an uncommon entity nowadays. A case of Lemierre's syndrome and co-infection with Mycoplasma pneumoniae is described, association published before in only 2 other cases. A 16-year-old girl with trombophlebitis of the left jugular vein, Fusobacterium necrophorum bacteremia and septic emboli in the lung requiring mechanical ventilation due to severe respiratory insufficiency. Despite early treatment with penicillin G and clindamycin, fever and part of pulmonary affectation persisted until that an antibiotic agent active against M. pneumoniae was instaurated, after its serological confirmation. The physicians should be easily recognized this disease because of its characteristic clinical findings, and co-infection with other organisms including M. pneumoniae, should be considered.