The article presents two clinical cases with description of peculiarities of septic infection occurred after splenectomy and due to congenital splenic hypoplasia.Decreased immune defense resulted from splenectomy leads to severe infections with a high risk of death. The most severe sequela is overwhelming postsplenectomy infection (OPSI-syndrome) which is characterized by high mortality rate (50-70%) within 12-24 hours from the onset of the first symptoms. The main risk factors of postsplenectomy sepsis are a condition which became an indication for splenectomy, the immune status of the patient, age and the time period after splenectomyStreptococcus pneumoniae, Haemophilus infuenzae type b, Neisseria meningitidis are commonly identified etiological factors of OPSI-syndrome. The diagnosis could be delayed due to nonspecific flu-like prodromal symptoms of the OPSI-syndrome. Delay in the diagnosis and treatment of sepsis may increase the risk of death.One of the syndromes associated with post-splenectomy sepsis is fulminant purpura (purpura fulminans), which requires differential diagnosis with meningococcal infection. However, half of the cases of fulminant pneumococcal purpura occur in patients with asplenia or hyposplenia. In the first clinical case, a preliminary diagnosis of generalized meningococcal infection was made on admission, but the diagnosis of pneumococcal infection could not be excluded in asplenic patient and was subsequently confirmed by laboratory tests.Given the high risk of fulminant postsplenectomy sepsis, and the difficulties of timely diagnosis, the preventive strategy of infections after splenectomy falls into three major categories- vaccination, antibiotic prophylaxis, and patient (patient’s parents) education.Improving healthcare workers’ knowledge is required to ensure prompt diagnosis of hyposplenism, adequate risk assessment of postplenectomy infection and prevention of OPSI-syndrome.