Objective: The aim of this study was to develop and psychometrically test the properties of the Self-care in Motor Neuron Disease (SCMND) Index., Methods: This instrument development and validation study was conducted in 3 phases. The first is to identify self-care behaviors in people with motor neuron disease (MND), and the second is to evaluate the content validity of the SCMND Index. Then, between March 2017 and March 2018, the tool was administered to 107 people with MND for psychometric tests., Results: The SCMND Index was developed based on the middle-range theory of self-care of chronic illness, including 15 self-care behaviors related to respiration, nutrition, mobility, medication, medical visits, and complication management. Content validity was excellent. Data analysis suggests that the instrument has a good internal consistency in all 3 domains and excellent reproducibility. Increased self-care behaviors' median values were associated with mechanical ventilation, cough assistance, and dysphagia. Domains differed significantly based on access (maintenance), hospital admissions (monitoring and management), and respiratory infection (management)., Conclusions: Self-care is a patient-centered outcome, and it is a key point of healthcare. Results suggest that the SCMND Index is useful for both clinicians and researchers to evaluate self-care in MND.