Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease, whose origin seems to lie in a acquired defect in the membrane of the pluri-potential hematopoietic cell. Chronic or intermittent acute hemolytic syndrome is the most frequent clinical manifestation, although in the literature there are also some references to the leukocytic and immunologic disorders of this disease. In this paper, we present the case of a 63-year-old patient with NPH who developed severe neutropenia and sustained febrile syndrome. In the past four years, she had suffered frequent episodes of fever and leukopenia, which apparently disappeared spontaneously. In the physical exploration, we observed hepatosplenomegaly. The hemogram showed mild iron deficiency anemia (hemoglobin 10.8 g/dl), severe neutropenia (neutrophil 0.3 x 10(9)/l) and significant reticulocytosis (610 x 10(9)/l). Iron deposits were greatly reduced in the marrow. Simultaneously to a new febrile episode and isolation of Escherichia coli in the urine, there was a severe anemization (hemoglobin 5 g/dl) and a significant thrombopenia (platelets 30 x 10(9)) resulting in a positive hemosiderinuria and sucrose test. The study of the leukocytic function showed a defect in the neutrophil chemotaxis, although a normal phagocytic capacity and microbicidal activity. In the following nine months, the patient had several severe infections, with intense but transitory pancytopenia, which always improved when treating the infection with antibiotics. The patient died due to a septic shock twelve months after the diagnosis. Recurrent febrile episodes and severe neutropenia are very rare in the PNH (less than 4% of the cases). The cause of these disorders is still unknown.(ABSTRACT TRUNCATED AT 250 WORDS)