Introduction: We report a prospective study of the effect of body mass index and the length of the tourniquet time on the blood loss in total knee replacement in 70 consecutive patients.

Methods and materials: The patients’ weight and height were recorded to establish the body mass index (BMI). The patients were classified into four groups according to their BMI. The blood loss both intra-operative and post-operative was recorded. In addition, the tourniquet time was recorded.

Results: No significant increase in blood loss was demonstrated in patients with a high BMI, and there was no significant increase in the blood loss with longer tourniquet times.

Conclusion: Obesity does not increase the overall bleeding in total knee replacement.