We report a prospective study of 1509 consecutive total knee arthroplasties looking at risk factors for infection in modern surgical practice. The overall deep infection rate was 1%. A further 51 patients had a superficial infection (3.3%). Statistical analysis revealed no correlation between risk of infection and age and sex. Those who had poor health as assessed by the American Society of Anesthesiologists score had no increased risk of infection. Neither did patients undergoing arthroplasty for rheumatoid arthritis. Diabetic patients and those with morbid obesity (body mass index, >40 kg/m(2)) had an increased odds ratio for deep and superficial infection, but these results did not reach statistical significance.