In this paper it is investigated if the mental computation strategies in the research literature are enough to satisfactorily categorize the mental computation strategy use by preservice elementary teachers (PETs) in subtraction on two-digit natural numbers. The PETs' use of mental computation strategies is measured operationally with a written questionnaire. The paper indicates that the strategies used by PETs are generally seen contained in the research literature on elementary school pupils' mental computation strategy use, but that there are additional strategies used by PETs, which are presented and discussed in the paper.