The insidious onset and occult characteristic of primary psoas abscess（PA） can cause diagnostic delays, resulting in high mortality and morbidity rates. In this article, three patients with PA accompanied with digestive malignancies visiting to my facility are reported. All patients had sever low back pain radiating to the ipsilateral foot, difficulty in walking over several days and suffered from high grade fever, malaise, loss of appetite. The presence of PA was examined by abdominal ultrasonography （AUS） and Computed tomography（CT）. PA was drainaged percutaneously or surgically. Postoperatively, those patients were administered antibiotics at another hospital. Culture of abscess of PA showed Streptococcus agalactiae in case 1, Escherichia coli
and Staphylococcus aureus in case 1 and case 2 respectively. One patient died of multiple organ failure. The present 3 patients were accompanied with digestive malignancies. There has been advocated some kinds of factors concerning about pathogenesis of PA. Furthermore, there has been reported some cases of PA accompanied with colon cancer. But there has been no case reports of PA accompanied with gastric cancer or hepatocellular carcinoma in the light of the literature inside and outside of Japan. Lumbar pain is a generally common disease, but we must pay attention to the existence of PA and search into its pathogenesis if we encounter the patient with sever lumbar pain, high grade fever. In conclusion, PA is a rare disease usually causing
misdiagnosis or delayed diagnosis. The present report is an instructive daily clinical experience.