The importance of surgical research has gained new prominence over the past decades as the relevance of well designed and well conducted studies has become increasingly evident. There are two basic but diametrically different methods of conducting research: the prospective randomized clinical trial and the retrospective surgical outcomes study based on administrative data. Administrative databases contain data that were initially collected for purposes other than scientific research. Whereas the prospective randomized clinical trial is familiar to most surgeons, surgical outcomes research based on administrative data constitutes a genre of investigation that is often unfamiliar to and even disparaged by the surgical community. In the present article, the strengths and weaknesses of both prospective randomized clinical trials and retrospective surgical outcomes research are discussed. Specifically, the advantages and limitations of investigations based on large administrative databases are outlined. Because both study designs play an important role in surgical research, carefully designed and implemented surgical outcomes research based on administrative data should be viewed as being complementary and not inferior to prospective randomized clinical trial