Improved TKA designs and surgical techniques have allowed surgeons to not only treat the pain associated with osteoarthritis but also to restore function. The present study analyzed whether the increase in physical activity of patients following surgery is associated with their level of functional and objective improvement. An activity questionnaire was utilized to collect pre- and post-operative information from 355 patients (417 knees). Corresponding functional and objective assessments were collected using the Knee Society rating system. Overall, a mean 48 point (range, -44 to 97 points) improvement in Knee Society function score showed moderate correlation to a 2.5 point (range, -40 to 57 points) increase in weighted activity score (R = 0.362). There was less of a correlation between the mean objective score increase of 49 points (-32 to 84 points) and change in activity level (R = 0.194). There were 29% of the patients who showed no change in activity level. These results suggest that change in activity level is more closely associated with improved function than changes in objective measures. With more than 52% of TKA patients reporting increased activity scores, further studies are needed to assess longer-term effects of activity levels on the durability of these prostheses.