This paper is part of a research done on Burnout Syndrome, and its objective is to develop and validate an instrument for measuring the syndrome in Secondary School teachers, taking as a principal starting point Maslach, Schaufeli, and Leiter's theory (2001). After developing and testing the instrument on a sample of 794 teachers in the Community of Madrid (Spain), we analyzed the reliability, content and construct validity (the latter by means of Structural Equations Models implemented with Software AMOS 7.0). The reliability analysis (α = .911 for the total instrument; .849, .899 and .674 for the dimensions of Exhaustion, Reduced Personal Accomplishment and Depersonalization respectively) and the Confirmatory Factorial Analysis (CMIN/DF = 4.163, CFI = .904, RMSEA = .60, PRATIO = .874) showed highly satisfactory results. The discrimination coefficient scores for items in the final instrument ranged between .22 and .74. Thus, the instrument presented combines the necessary technical characteristics for it to be considered a valid and reliable tool for measuring the syndrome.