Pulmonary embolism is a serious complication after arthroscopy of the knee, about which there is limited information. We have identified the incidence and risk factors for symptomatic pulmonary embolism after arthroscopic procedures on outpatients. The New York State Department of Health Statewide Planning and Research Cooperative System database was used to review arthroscopic procedures of the knee performed on outpatients between 1997 and 2006, and identify those admitted within 90 days of surgery with an associated diagnosis of pulmonary embolism. Potential risk factors included age, gender, complexity of surgery, operating time defined as the total time that the patient was actually in the operating room, history of cancer, comorbidities, and the type of anaesthesia. We identified 374 033 patients who underwent 418 323 outpatient arthroscopies of the knee. There were 117 events of pulmonary embolism (2.8 cases for every 10 000 arthroscopies). Logistic regression analysis showed that age and operating time had significant doseresponse increases in risk (p < 0.001) for a subsequent admission with a pulmonary embolism. Female gender was associated with a 1.5-fold increase in risk (p = 0.03), and a history of cancer with a threefold increase (p = 0.05). These risk factors can be used when obtaining informed consent before surgery, to elevate the level of clinical suspicion of pulmonary embolism in patients at risk, and to establish a rationale for prospective studies to test the clinical benefit of thromboprophylaxis in high-risk patients.