Bus SA, Waaijman R, Nollet F. New monitoring technology to objectively assess adherence to prescribed footwear and assistive devices during ambulatory activity. Objective To assess the validity and feasibility of a new temperature-based adherence monitor to measure footwear use. Design Observational study. Setting University medical center and participants' homes. Participants Convenience sample of healthy subjects (n=11) and neuropathic diabetic patients at high risk for foot ulceration (n=14). Interventions In healthy subjects, the validity of the in-shoe attached adherence monitor was investigated by comparing its registrations of donning and doffing of footwear during 7 days to an accurately kept log registration. In diabetic patients, the feasibility of using the adherence monitor for 7 days in conjunction with a time-synchronized ankle-worn step activity monitor to register prescribed footwear use during walking was assessed. Furthermore, a usability questionnaire was completed. Main Outcome Measures For validity, the mean time difference and 95% confidence interval (CI) between moments of donning/doffing footwear recorded with the adherence monitor and in the log were calculated. For feasibility, technical performance, usability, and the percentage of steps that the footwear was worn (adherence) were assessed. Results The mean time difference between the adherence monitor and log recordings was 0.4 minutes (95% CI, 0.2–0.6min). One erroneous recording and 2 incomplete recordings were obtained in diabetic patients. Three patients reported discomfort with the step activity monitor, and 4 patients would not favor repeated testing. Patients used their footwear for between 9% and 99% of their walking steps. Conclusions The adherence monitor shows good validity in measuring when footwear is used or not, and is, together with instrumented monitoring of walking activity, a feasible and objective method to assess treatment adherence. This method can have wide application in clinical practice and research regarding prescribed footwear and other body-worn assistive devices.