Obesity has been shown to be a risk factor for knee osteoarthritis. Total knee arthroplasty in the obese patient has given rise to some controversy in terms of perioperative risks, and the longevity of the implants. We reviewed the salient literature on this subject regarding the impact of obesity on the knee, the outcome of TKA in the obese patient, and on the effect of TKA on pre-existing obesity. While increased risk of complications and early implant failure has been shown by some studies in the morbidly obese, there is no definite cut-off in Body Mass Index which accurately separates high-risk from low-risk individuals, although there is evidence that heavier patients are at greater risk. We have seen that although postoperative scores are lower in the obese group, these patients may derive considerable improvement in pain following TKA. While not condoning the obese patient with knee arthritis being denied an effective pain-relieving procedure, we stress the importance of appropriate risk-counselling of these patients, and allowance within the healthcare system for the extra financial and service implications placed by the obese TKA patient.