In a retrospective study in an academic, acute-care community hospital, we studied the possible safety and effectiveness of a practice guideline recommending early discharge from the hospital for patients having uncomplicated total knee replacement. Of 206 patients receiving knee replacements, 162 (79%) were classified by the guideline as being at low risk for complications between the 4th and 7th postoperative days. Use of the guideline could have reduced the postoperative length of stay from 7.3 +/- 2.6 days to 4 days for the 112 patients (54%) who became low risk on the 4th postoperative day. Explicit and implicit review of the quality of care determined that 157 patients (96.9%; 95% confidence interval, (92.9%, 99.0%) could have been safely transferred from the acute-care hospital to an appropriate setting when they became classified at low risk between the 4th and 7th postoperative days. Clinical practice guidelines can possibly be used to reduce the postoperative length of acute-care hospital stay for patients having knee replacements. This guideline requires further study in a controlled clinical trial before it can be recommended for use.