We report the fourth case of Lyme borreliosis in a man infected with human immunodeficiency virus (HIV). The erythema chronicum migrans was persistent, overlapping with meningoradiculitis. Repeated immunofluorescence tests for Borrelia burgdorferi sensu lato remained negative in both sera and cerebrospinal fluid (CSF), the enzyme-linked immunosorbent assay was weakly positive in serum and CSF and a Western blot was positive. The skin infiltrate was composed mostly of T lymphocytes with a CD4/CD8 ratio of 0.5. The course of the disease was favourable after treatment with intravenous ceftriaxone. Further studies are necessary to evaluate whether HIV infection influences, as does syphilis, the course and response to treatment of Lyme borreliosis. Serological tests are insufficiently sensitive and the Western blot assay is necessary to confirm Lyme disease in HIV-positive patients.