Study Design. Compliance monitor measurement of orthosis wearing time during laboratory climate tests and normal volunteer subject tests were compared to normal diaries. Objective. To develop and test the accuracy and reliability of a device designed to measure spinal orthosis wearing time. Summary of Background Data. Orthosis wearing time is an important factor in orthotic treatment for spine disorders. A reliable and objective method for measuring orthosis wearing time currently is lacking. Methods. Four pressure switches and a data logger embedded in each thoracolumbosacral orthosis recorded orthosis wearing time. Orthoses were assumed to be worn when at least two switches were “on.” Laboratory climate tests and normal volunteer tests were conducted to assess the ability of the compliance monitor to measure orthosis wearing time. A manual wearing-event diary was kept during all the tests. The length of each wearing-time interval, the daily wearing time, and the cumulative wearing time were calculated from data recorded by the compliance monitor and the manual diaries. Results. A linear regression was performed on all orthosis wearing-time intervals as recorded by the compliance monitor and by the manual diaries. Climate chamber tests yielded 121 sensor trigger-event intervals (R2 = 0.998; slope = 1.003;P < 0.0001). Normal subject testing yielded 72 orthosis wearing-time intervals (R2 = 0.998; slope = 0.998;P < 0.0001). Conclusion. As indicated by the regression analyses, the compliance monitor accurately quantified the orthosis wearing-time intervals during the laboratory climate tests and the tests with normal volunteers.