The aim of this study is to determine whether clinicians' estimates of patients' walking time agree with those determined by accelerometer devices. The walking time was measured using a waist-mounted accelerometer device everyday during the patients' waking hours. At each weekly meeting, clinicians estimated the patients' average daily walking time in the previous week. Twenty-eight clinicians completed 176 estimates of the average daily walking time for 13 patients (78.5 plus or minus 6.6 years old) over 31 weeks. The average daily walking time measured by the accelerometers was 36.4 plus or minus 16.2 min and that estimated by clinicians was 61.3 plus or minus 38.4 min. Clinicians overestimated the amount of walking time by 24.8 min on average (mean% error = 165.8%). Most estimates were between an hour less to 2 h more than the accelerometer measurements. Only 38.6% of the estimates agreed with the accelerometer measurements. Therefore, clinician assessment of the level of patient activity in a rehabilitation setting is highly inaccurate and unreliable. (Contains 1 figure and 1 table.)