OBJECTIVE: Anti-Coagulant therapy is often prescribed for patients in the hospitals who are at high risk for a deep vein thrombosis or pulmonary embolism (DVT/PE). The purpose of this study is to determine if there are better outcomes for patients who start anti-coagulant therapy on day one as opposed to later in their stay. METHODS:  A retrospective study was conducted with 391,253 patients who had Lovenox discharged between January 2001 through June 2005 extracted from Solucient's ACTracker Database and grouped into a cohort of 206,456 patients who received the drug on day one and a group of 184,797 patients who received the drug afterwards as the comparison group. Economic and clinical outcomes were measured with the following metrics by different risk adjust methods 1). length of stay (LOS), ICU LOS, and total costs within risk adjusted RDRGs, as well as 2). the results of Risk-Adjusted Mortality (RAMI) and Complication (ECRI) indices. RESULTS: In comparing those patients who received an anti-coagulant on the first day versus anytime after, we found that day one treated patients had significantly shorter weighted average and  ICU weighted average LOS with a difference of 0.87 days (p<0.0001) and 0.40 days (p<0.0001)  on average respectively. A significantly decreased weighted average total cost in patients receiving the drug earlier was also observed with a difference of $806 (p<0.0001). In clinical perspectives, earlier treated Lovenox patients were found to have both lower mortality index (0.96 vs. 1.04, p<0.0001) and lower complication rates (0.94 vs. 1.05, p<0.01). CONCLUSION: Patients who received prophylaxis anti-coagulant therapy on their first day of an inpatient stay have better economic and clinical outcomes than those who receive anti-coagulants later in their stay.