A case of acute transverse myelopathy with anaesthesia and flaccid paralysis of both lower limbs, following intragluteal penicillin injection, is reported. This accident was probably due to a mistaken intra-arterial injection of the drug with retrograde progression through branches of the internal iliac artery up to the spinal cord. The treatment of such events in all the cases reported by the literature has been disappointing. Therefore, particular precautions must be taken in case of intramuscular penicillin injection, according to the present and the previous cases described, in order to avoid such accidents.