Splenic abscess is a rare condition, with peak incidence in the third and sixth decade of life. It is significantly less common in children than in adults. The main causes of abscess include multiorgan infections, immune deficiency, and trauma. Coexisting diabetes, infective endocarditis and immune deficiency are adverse prognostic factors. Aetiological factors of splenic abscess include aerobic and anaerobic bacteria and fungi. The symptoms of splenic abscess are non-specific and include abdominal pain in the upper-left-quadrant, fever, splenomegaly, and increased inflammatory markers. The diagnosis is confirmed by abdominal sonographic and computed tomography findings. Conservative (antibiotic therapy) and surgical (drainage and splenectomy) treatment is used. Splenic abscess is an exceptionally dangerous condition in which early, correct diagnosis and treatment can reduce mortality from several dozen to less than 10%. The presented case illustrates the course of disease in a 6-year-old boy, emphasising the need to include splenic abscess in the differential diagnosis of fever of unknown origin.