BACKGROUND: Patients are playing an increasingly large role in their own management and must therefore receive clear, complete, and comprehensible information. In the field of hip and knee arthroplasty, little is known about the level of patient knowledge and effectiveness of surgeon-to-patient information transfer. We therefore designed a prospective observational study with the objective of assessing four factors: patient knowledge during management, quality of information transfer, informational needs, and factors associated with the level of knowledge. HYPOTHESIS: The level of patient knowledge changes during the management process. PATIENTS AND METHODS: A prospective single-centre study was conducted between January 2014 and March 2015 during the outpatient visits and inpatient stays of 63 patients who underwent arthroplasty of the hip (n=36) or knee (n=27). A single observer attended all patient visits and recorded the information provided by the surgeon. Each patient completed a self-questionnaire after the outpatient visit (T1), at admission (T2), and at discharge after surgery (T3). Semi-quantitative scores were used to assess knowledge and informational needs. The effectiveness of information transfer was evaluated by comparing the information provided by the surgeon to the replies made by the patients. RESULTS: The mean overall knowledge score (on a 0-42 scale) increased from 17.22±6.33 at T1 to 19.44±6.89 at T3 (P=0.0028). In contrast, knowledge about complications was better at T1 than at T3 (2.67±1.98 vs. 2.19±1.91; P<0.05). Agreement between information given by the surgeon and replies made by patients varied across items from 23% to 100%. The mean informational needs score (on a scale from 0 to 21) ranged from 3.67 to 4.83 and was higher at T3 than at T2 (4.83±3.77 vs. 3.67±4.86; P=0.03). The proportion of patients who wanted written information was higher at T3. Most patients sought information before the outpatient visit. At each step of the management process, the main areas about which the patients wanted information were the surgical procedure, the rehabilitation programme, and the prosthesis. Several socio-demographic or management-related factors influenced the level of knowledge. Thus, older age and lower educational attainment were associated with lower knowledge scores, whereas previous lower-limb orthopaedic surgery and amount of information provided by the surgeon were associated with higher knowledge scores. Knowledge scores were not associated with being employed vs. retired, gender, replacement of a hip vs. a knee, the surgeon, or being accompanied by another person. DISCUSSION: Our study is original in that we assessed changes in patient knowledge during the management process for hip or knee arthroplasty. The level of patient knowledge was fairly low and varied considerably across individuals and time points in the management process. These data highlight the importance of providing patients with information throughout their management and particularly at discharge, when the desire for information seems greatest. LEVEL OF EVIDENCE: IV, prospective observational study with no control group.