Few studies have been published assessing patients sporting activity after total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA). Common concerns of patients undergoing TKA or UKA are whether they can continue with sporting activities after surgery. This study compares the sporting activity of TKA and UKA patients preoperatively and postoperatively. A total of 110 patients were surveyed by questionnaire. Seventy-six patients had undergone TKA and 34 patients had undergone UKA. They were assessed for their participation in low-impact sport preoperatively and postoperatively at a mean follow up of 21.6 ± 5.3 and 22.3 ± 7.8 months, respectively. Low-impact sports are those which a surgeon would expect patients to be able to participate in postoperatively. Data were separately analysed for older and younger patients and women and men, respectively. The results were as follows: before surgery, 55 of 76 patients in the TKA group participated in an average of 1.3 different sports and postoperatively, 35 of 76 patients participated in an average of 0.7 different sports. In the UKA group, 30 of 34 patients participated in an average of 1.5 different sports preoperatively and postoperatively, 29 of 34 patients participated in an average of 1.4 different sports. The return to sport rate was 96.7% in the UKA group and 63.6% in the TKA group. In the TKA group, the average frequency of sport preoperatively was 3.0 sessions per week (62.7 min) and postoperatively it decreased to 2.0 sessions per week (37.5 minutes). In the UKA group, the average frequency of sport preoperatively was 3.2 sessions per week (85.0 min) and postoperatively it increased to 3.4 sessions per week (92.1 min). The average time before resuming sport after surgery was 4.1 months in the TKA group and 3.6 months in the UKA group; 42.9% of patients in the TKA group and 24.1% of patients in the UKA group reported pain during sports after surgery; 80.3% of the patients in the TKA group and 88.2% of the patients in the UKA group felt that surgery had increased or maintained their sporting ability. Oxford knee scores decreased significantly one year after surgery in both the TKA group and the UKA group. In conclusion, the patients in our study had a significantly greater return to sport rate after UKA than patients who had undergone TKA. A large proportion of patients in the TKA group did not return to sport which their surgeon would have expected them to including golf and bowls. Patients in the UKA group also took part in more sporting sessions and for a longer period of time than patients in the TKA group. Moreover, patients undergoing UKA also returned to sport more quickly than patients undergoing TKA.