Malignant external otitis (MEO) is an infrequent but severe infective disorder, generally due to Pseudomonas aeruginosa, which most often affects elderly diabetics patients. The clinical features rarely permit exact diagnosis of MEO to be made promptly, and initially at least they are difficult to distinguish from those of external otitis. This explains the frequent delay in diagnosis with respect to the onset of symptoms. Physical examination almost always reveals the presence of aspecific granulation tissue in the external auditory canal, while the most common laboratory finding is raised erythrocyte sedimentation rate (ESR). Imaging has great diagnostic relevance: CT and MRI are very useful for spatial resolution, while radionuclide scanning and, in our experience, SPECT are superior for detecting early osteitis and monitoring response to therapy. We present an extensive review of the literature and our personal experience. In particular, we stress the relevance of immunological study of MEO patients: all our 4 patients had defective immune defences. As regards therapy, like other authors we underline the fundamental importance of long-term antibiotic treatment. The availability of quinolones and latest generation cephalosporins has greatly simplified the choice of antibiotic treatment, although clinicians should be aware of the possibility of drug-resistant bacterial strains.