Thinking styles of students in problem solving environments is an important theme for mathematics education researches. Specifically, to determine students' preferences in mathematical problem solving situations give teachers clues about learning practices of students which are important for effective course plans, classroom activities and tasks. The aim of this study is to evaluate the validity and reliability of Mathematical Processing Instrument (MPI) which was developed by Norma Presmeg (1985) in the USA for Turkey's education conditions. As a part of the study, section B -developed especially for teachers of mathematics at high school - is translated into Turkish; and its validity and reliability is evaluated. (C) 2010 Elsevier Ltd. All rights reserved.