We asked whether there was an association between obesity levels and subsequent THA or TKA using data from 54,406 THA and TKA patients entered into the Canadian Joint Replacement Registry. We compared these patients with a sample of the Canadian population using the Canadian Community Health Survey of 2006. We analyzed information from the Canadian Joint Replacement Registry to quantify the relative risk for THA or TKA in Canada for specific body mass index categories. In reference to the acceptable weight category of body mass index less than 25 kg/m2, the risk for TKA and THA was 3.20- and 1.92-fold higher, respectively, for overweight individuals (body mass index 25-29.9 kg/m2); 8.53- (TKA) and 3.42-fold (THA) higher for those in the obese Class I (body mass index 30-34.9 kg/m2) category; 18.73- (TKA) and 5.24-fold (THA) higher for those identified in obese Class II (body mass index 35-39.9 kg/m2); and 32.73- (TKA) and 8.56-fold (THA) higher for people in obese Class III group (body mass index > 40 kg/m2). Thus, our data support an association between obesity and subsequent THA and TKA.