Researchers have been concerned about the psychometric limitations of the some previous questionnaires designed to evaluate burnout. To address these problems associated with previous instruments, the Spanish Burnout Inventory (SBI) was developed. The instrument has not yet been validated in staff nurses. The purpose of this paper was to evaluate the psychometric properties of the SBI. The sample consisted of 720 staff nurses from two Spanish general hospitals. The instrument is composed of 20 items distributed in four dimensions: Enthusiasm towards the job (five items), Psychological exhaustion (four items), Indolence (six items) and Guilt (five items). Data were subjected to confirmatory factor analysis. To assess the factorial validity of the SBI, four alternative models were tested. Results show that the four-factor model of the SBI has adequate psychometric properties for the study of burnout in staff nurses. This model fitted the data better than the alternative models. The study provides evidence of the adequate psychometric properties of a measure to evaluate burnout in nursing professionals. The SBI proposes a theoretical explanation for the different types of burnout, facilitating the diagnosis and treatment of staff nurses.