Purpose: To evaluate the diagnostic efficacy of ultrasonographically (US) guided percutaneous core biopsy of reticular infiltrations alone without mass in the mesentery and omentum at contrast material-enhanced abdominal computed tomography (CT). Materials and Methods: This study was approved by the institutional review board, and the need for obtaining signed informed consent was waived for this retrospective analysis. From March 2004 to May 2009, 45 patients (mean age, 52.3 years; age range, 21-89 years) with reticular infiltrations alone without mass in the mesentery and omentum at contrast-enhanced abdominal CT underwent US-guided percutaneous core biopsy. Twenty-one men and 24 women were included. The area with the severest infiltrations at CT was targeted during real-time US-guided percutaneous biopsy. Biopsy results were compared with the final results of surgery or follow-up. The diagnostic accuracy of US-guided percutaneous biopsy was then calculated. Results: One patient had an insufficient biopsy specimen. Among the 44 patients with sufficient biopsy specimens, 17 patients had malignancy, 12 had tuberculosis, and 15 had nonspecific inflammation. All 29 patients with malignancy and tuberculosis at biopsy had that confirmed with surgery or follow-up results. Two of 15 patients with nonspecific inflammation at percutaneous biopsy were confirmed as having malignancy at surgery and four as having tuberculosis after improvement with empirical antituberculosis therapy. The diagnostic accuracy of US-guided percutaneous biopsy of reticular infiltrations in the mesentery and omentum was 84%; the sensitivity and specificity was, respectively, 89% and 100% for malignancy, 75% and 100% for tuberculosis, and 90% and 83% for nonspecific inflammation. Conclusion: US-guided percutaneous core biopsy is a feasible diagnostic method with high specificity for confirmative diagnosis of reticular infiltrations alone in the mesentery and omentum at contrast-enhanced CT.