A prospective, blinded, randomised controlled trial investigated the effectiveness of quadriceps exercises following anterior cruciate ligament reconstruction. A treatment group (Quadriceps exercise group) performed straight leg raises and isometric quadriceps contractions throughout the first two postoperative weeks, and a second group (No quadriceps exercise group) did not. A battery of outcome measures assessed subjects postoperatively at day one, two weeks, and one, three and six months. A total of 103 patients (Quadriceps exercise n = 48, No quadriceps exercise n = 55) commenced the study with 91 subjects available at final follow up (Quadriceps exercise n = 47, No quadriceps exercise n = 44). Performance of quadriceps exercises significantly improved a number of knee flexion and extension range of motion measurements (p = 0.01 to 0.04). No significant differences were found between the two groups at any postoperative period for quadriceps lag (p = 0.36), functional hop testing (p = 0.49 to 0.51), isokinetic quadriceps strength (p = 0.70 to 0.72), the majority of numerical analogue scores (p = 0.1 to 0.94) and Cincinnati scores (p = 0.10 to 0.84). Subjects performing quadriceps exercises reported significantly higher pain scores with exercise on the first postoperative day (p = 0.02). At six months postoperatively, the Quadriceps exercise subjects reported significantly more favourable Cincinnati scores for symptoms (p = 0.005) and problems with sport (p = 0.05). While average knee laxity was not significantly different between treatment groups over time (p = 0.27 to 0.94), quadriceps exercise performance was associated with a significantly lower incidence of abnormal knee laxity. Isometric quadriceps exercises and straight leg raises can be safely prescribed during the first two postoperative weeks and confer advantages for faster recovery of knee range of motion and stability. It remains to be proven whether the magnitude of differences between groups is clinically significant.