In a prospective single-centre longitudinal randomized controlled trial 116 patients were allocated to the sub-vastus approach, and 115 to the medial parapatellar approach. At one week follow-up, compared to baseline, range of motion, Knee Society (KS) global, KS knee, and KS pain scores were significantly better in the sub-vastus group. At the one year follow-up, WOMAC global and pain scores, SF36 physical function and role-physical scores, and EuroQol utility and pain score were significantly better in the sub-vastus group. The ease of exposure in the sub-vastus approach was significantly worse. There was no significant difference in length of stay or analgesia intake. The sub-vastus approach to total knee arthroplasty was more effective than a medial parapatellar approach at both one week and one year post-operatively, but surgeons reported a less easy exposure in the sub-vastus group.