A 43-year-old diabetic woman on peritoneal dialysis, developed left upper abdominal pain and culture-negative cloudy peritoneal dialysate. The dialysate had WBC counts of 1,532/µL with 90% polymorphonuclear cells. The patient did not respond well to anti-bacterial therapy. Abdominal CT scan revealed diffuse atherosclerosis in the abdominal vessels and wedge-shaped splenic infarction. Anticoagulation therapy was initiated and an improvement in peritonitis was observed without peritoneal catheter removal. Thus, in peritoneal dialysis patients with diffuse atherosclerosis or the risk of systemic embolization, symptoms of unexplained left upper quadrant pain and culture-negative peritonitis should be evaluated to rule out splenic infarction.