The authors present a case of pneumonia by Friedlander's bacillus. They emphasize its main complieations and prognostic, describing the natural history of the disease and radiological picture, because they are important clues for the diagnosis. An analysis of the principal radiological signs of the condition is carried out and considered for differential diagnosis. They call attention for the multiplicity of microorganisms able to produce pulmonary necrosis, and finally state the role of Klebsiella as an etiological agent in the today's hospital infections, also giving a therapeutic approach for the acute forms.