The mathematics teaching efficacy beliefs of preservice elementary teachers have been the subject of several studies. A widely used measure in these studies is the Mathematics Teaching Efficacy Beliefs Instrument (MTEBI). The present study provides a detailed analysis of the psychometric properties of the MTEBI using Bayesian item response theory. We discuss local dependence between item pairs, psychometric quality of the items, validity of the scoring procedure, and measurement accuracy for teachers with different efficacy levels. Our findings suggest that in its present form, the test reliability of the MTEBI may not be as high as assumed to date. The scale, wording, and placement of the items need revision. Moreover, additional items need to be constructed to measure below average levels of efficacy more accurately. Ordering the items according to difficulty, we describe the structure of mathematics teaching efficacy beliefs and draw some implications for mathematics teacher educators. (Contains 2 figures and 5 tables.)