The instrument to assess the adherence of adult patients to long-term functional neurorehabilitation processes, Scale to Measure Adherence to the Neurorehabilitation (SMAN), based on the dimensions of the World Health Organization (WHO), constitutes the first step in the deepening and analysis, from a psychometric perspective, of the problem of lack of adherence to treatment in functional neurorehabilitation. Objective: To design an instrument for evaluating the adherence of adult patients to long-term functional Neurorehabilitation processes, based on the WHO dimensions, and to evaluate it in its internal validity and content characteristics. Patients and Method: For the internal consistency tests, 100 adult patients with a diagnosis of neurological injury participated, a non-probabilistic sampling of type subjects was carried out. For the content validity tests, the participation of health professionals dedicated to Functional Neurorehabilitation was included. Internal consistency tests were applied to validate the instrument through Cronbach's alpha coefficient. Results: The Cronbach's Alpha value, taking into account all the factors and each of the items of the SMAN instrument, was 0.835, which shows good internal consistency or longitudinal validity. Conclusions: The factorial structure of the SMAN resulting from this research and the items that compose it, show a satisfactory reliability demonstrated through internal consistency tests where homogeneity of the instrument was evidenced, demonstrating the degree to which the elements that make up the scale measure the same concept.