To determine if extended scope physiotherapists perform to the same standards as their orthopaedic colleagues with regards to diagnosing knee pathology and making appropriate referrals for arthroscopy. Data was collected prospectively from Aug 2005. Patients were seen in a consultant led orthopaedic clinic by an Extended Scope Physiotherapist (ESP), a registrar or the consultant. All patients placed onto the waiting list for knee arthroscopy were considered for the study. The outpatient diagnosis and demographic data were recorded and compared against the arthroscopy findings. A single consultant surgeon performed the arthroscopies. 300 patients were included in the study (100 in each group). Each group was similar in terms of presenting complaint and demographics. There was no significant difference between the ESP’s and registrars in their ability to diagnose intraarticular pathology (CHI squared test: X 2.031, df 1, p=0.15). When only cruciate and meniscal pathology were considered there was also no significant difference between the ESP’s and the registrars (Fishers test p=0.12 and p=0.22 respectively, 2-tail test) The ESPs performed particularly well in their ability to diagnose cruciate injuries (sensitivity 100%, specificity 100% and PPV 100%). Both ESPs and registrars had high sensitivity but low specificity with regards to diagnosing meniscal pathology suggesting a low threshold for a positive diagnosis and a poor ability to correctly diagnose those patients who did not have a meniscal injury. Of the 300 patients only 9 unnecessary arthroscopies were requested. None were requested by the ESPs. Extended scope physiotherapists perform a useful role in orthopaedic outpatients. They perform as well as orthopaedic registrars with regards to making the correct diagnosis and the selection of patients for arthroscopy.