Exhibit 21 ---------- SUBSIDIARIES OF THE REGISTRANT ------------------------------ Name State of Organization - ---- --------------------- US Oncology Corporate, Inc, Delaware AOR Real Estate, Inc. Delaware RMCC Cancer Center, Inc. Delaware AOR Management Company of Indiana, Inc. Delaware AOR Holding Company of Indiana, Inc. Delaware AOR of Indiana Management Partnership Indiana AOR Management Company of Oregon, Inc. Delaware AOR Management Company of Missouri, Inc. Delaware AOR Management Company of Arizona, Inc. Delaware AOR Management Company of Oklahoma, Inc. Delaware AOR Management Company of South Carolina, Inc. Delaware AOR Management Company of Pennsylvania, Inc. Delaware AOR Management Company of North Carolina, Inc. Delaware AOR Management Company of Virginia, Inc. Delaware AOR Management Company of New York, Inc. Delaware AOR Management Company of Florida, Inc. Delaware AOR Management Company of Nevada, Inc. Delaware AOR Management Company of Texas, Inc. Delaware AOR Management Company of Ohio, Inc. Delaware AOR Management Company of Kansas, Inc. Delaware AOR Management Company of Central Florida, Inc. Delaware AORT Holding Company, Inc. Delaware AOR of Texas Management Limited Partnership Texas AORIP, Inc. Delaware AOR Synthetic Real Estate, Inc. Delaware Greenville Radiation Care, Inc. Delaware Physician Reliance Network, Inc. Texas TOPS Pharmacy Services, Inc. Texas US Oncology Research, Inc. Texas Physician Reliance Investments, LLC Delaware PRN Physician Reliance, LLC Texas Physician Reliance, L.P. Texas AOR Management Company of Alabama, Inc. Delaware