PURPOSE: The aims of this study were to quantify the frequency of adverse outcomes after elective knee arthroscopies in Victoria, Australia, and to identify risk factors associated with adverse outcomes. METHODS: We performed a retrospective, longitudinal cohort study of elective orthopaedic admissions using the Victorian Admitted Episodes database, a routinely collected public and private hospital episodes database linked to death registry data, from July 1, 2000, to June 30, 2009. Adverse outcome measures included pulmonary embolism (PE), deep vein thrombosis (DVT), hemarthrosis, effusion and synovitis, cellulitis, wound infection, synovial fistula, acute renal failure, myocardial infarct, stroke, and death. Patients were excluded if they had an additional procedure performed during the arthroscopy admission. We identified complications during the admission and within readmissions up to 30 days after the procedure. PE, DVT, and death within 90 days of the arthroscopy episode were also examined. We used logistic regression analysis to identify risk factors associated with complications. RESULTS: After we excluded 16,807 patients (8.5%) with an additional procedure during their admission, there were 180,717 episodes involving an elective arthroscopy during the period studied. The most common adverse outcomes within 30 days were DVT (579, 0.32%), effusion and synovitis (154, 0.09%), PE (147, 0.08%), and hemarthrosis (134, 0.07%). The 30-day orthopaedic readmission rate was 0.77%, and there were 55 deaths (0.03%). Within 90 days of arthroscopy, we identified 655 events of DVT (0.36%) and 179 PE events (0.10%). Logistic regression analysis identified that potential risk factors for complications were older age, presence of comorbidity, being married, major mechanical issues, and having the procedure performed in a public hospital. CONCLUSIONS: Our study found 6.4 adverse outcomes per 1,000 elective knee arthroscopy procedures (0.64%), with the 3 most common complications being DVT, effusion and synovitis, and PE. We have also identified risk factors for adverse outcomes, particularly chronic kidney disease, myocardial infarction, cerebrovascular accident, and cancer. LEVEL OF EVIDENCE: Level III, retrospective cohort study.