Updated project metadata. Vaccine-enhanced disease (VED) occurs as a result of vaccination followed by infection with virulent Mycoplasma pneumoniae. To date, VED has prevented development of an efficacious vaccine against this significant human respiratory pathogen. Herein we report that vaccination with M. pneumoniae lipid-associated membrane proteins (LAMPs) induces lung lesions consistent with exacerbated disease following challenge, without reducing bacterial loads. Removal of lipid moieties from LAMPs prior to vaccination eliminates VED and reduces bacterial loads after infection. Collectively, these data indicate that lipid moieties of lipoproteins are the causative factors of M. pneumoniae VED.