Abstract The purpose of this investigation was to determine whether functional performance and self-report outcomes are related to body mass index (BMI) after total knee arthroplasty (TKA). We hypothesized that higher BMIs would negatively affect functional performance as assessed by the timed up-and-go test, stair climbing test, 6-minute walk test, and self-report questionnaires. A total of 140 patients with BMIs ranging from 21.2 to 40.0 kg/m 2 were followed over the first 6 months after unilateral TKA. Hierarchical linear regression was used to evaluate the impact of BMI on functional performance at 1, 3, and 6 months after TKA, while taking into account preoperative functional performance. There were no meaningful relationships between BMI and functional performance in the subacute (1 and 3 months) and intermediate (6-month) stages of recovery.