We describe a case with no neurological signs but marked psychiatric symptoms induced by borrelia burgdorferi, whose clinical picture was indistinguishable from an endogenous schizophrenia. The symptoms within one week under antibiotic treatment with ceftriaxon, but afterwards the patient showed a mild organic brain syndrome. The case demonstrated the aetiologic nonspecificity of paranoid symptoms and hallucinations and emphasizes that in psychotic patients without psychiatric history additional diagnostic measures should be performed.