Thirty knees in 27 obese patients were matched to 30 knees in 27 nonobese patients, with both cohorts followed for a mean of approximately 15 years. Nine of 30 obese knees were revised, whereas 3 of 30 nonobese knees were revised, with Knee Society objective scores being higher in the nonobese group. There were more polyethylene insert revisions in the nonobese group, which may have been accounted for by a trend of higher activity levels in this group. The authors concluded that at long-term follow-up, although not statistically significant, there was a trend for obesity to influence the rate of aseptic loosening. This may occur because of increasing stress at the bone-prosthesis interface, whereas increased activity levels in the nonobese patients may adversely affect the longevity of the polyethylene insert.