Total knee arthroplasties are at risk for hematogenous seeding secondary to procedures that create a transient bacteremia. To define the risk of infection associated with dental surgery, a retrospective review of the records of 3490 patients treated with total knee arthroplasty by the authors between 1982 and 1993 was performed. Sixty-two total knee arthroplasties with late infections (greater than 6 months after their procedure) were identified, and of these, seven infections were associated strongly with a dental procedure temporally and bacteriologically. These seven cases represented 11% of the identified infections or 0.2% of the total knee arthroplasty procedures performed during this period. In addition, among 12 patients referred for infected total knee arthroplasties from outside institutions, two infections were associated with a dental procedure. Five of the nine (56%) patients had systemic risk factors that predisposed them to infection, including diabetes and rheumatoid arthritis. All dental procedures were extensive in nature (average, 115 minutes; range, 75-205 minutes). Eight of the patients received no antibiotic prophylaxis. One patient had only one preoperative dose. Infections associated with dental procedures may be more common than previously suspected. Eight of these patients had no prophylactic antibiotics, and one had inadequate coverage. The authors think that patients with a total knee arthroplasty who have systemic disease that compromises host defense mechanisms against infections and who undergo extensive dental procedures should receive prophylactic antibiotics. A first generation cephalosporin, given 1 hour preoperatively and 8 hours postoperatively would provide the best prophylaxis against the organisms identified in this study.