There are a few papers in the literature to indicate the likely functional outcome of conservatively managed sportsmen in whom primary outcome cruciate ligament [ACL] healing occurs. We reviewed 298 sportsmen presenting with isolated ACL rupture that were conservatively managed with a rehabilitation programme, based on regaining proprioceptive and hamstring control, and aimed at achieving primary ACL healing. All were protected in a hinged brace. In 50 patients, the ACL was determined as having healed clinically; these patients underwent instrumented laximetry testing with KT 1000 arthrometry and were determined: IKDC A [Normal] or IKDC B [nearly normal]. An MRI was also performed which confirmed healing in 39 patients with ACL fibres parallel to Blumenstat's line. In 11 patients the ACL stump had healed to the PCL. The 50 patients were followed up for an average 16 months [range, 14 to 17 months]. 56% of patients suffered recurrent instability when they returned to their preinjury level of contact or pivoting sport. For competitive athletes, 76.5% suffered further instability on return to sport despite the four-month rehabilitation and independent arthrometry score or MRI findings. However, for occasional, recreational athletes only 7% suffered recurrent instability. This study suggests that a rehabilitation programme aimed at primary ACL healing affords satisfactory results for the occasional, recreational athlete but does not achieve the quality of restraint sufficient for contact or pivoting sports in competitive athletes. These patients suffer high levels of recurrent instability and are exposed to the risk of secondary chondral and meniscal injury