Splenic abscess is a rare condition. Haematogenous seeding to the spleen from an infection at a distant site, most often endocarditis, is been the most common predisposing condition but an increase has been observed in immuno-compromised patients too. Fever, leukocytosis and left upper quadrant pain are suggestive, but the signs and symptoms of splenic abscesses are often non-specific. Rare is the onset with diarrhoea as in our case. Ultrasound and computed tomography are reliable diagnostic tools. Splenectomy and antibiotics are the treatments of choice. We describe a case of splenic abscess with gas level and peritonitis from dissemination of Streptococcus anginosus (of Streptococcus millerii group) from duodenal ulcer contaminated. It was diagnosed with CT, ultrasound, and abdomen X-ray with contrast then treated with splenectomy and peritoneal lavage.