The purpose of this research was to determine physics teachers' assessment methods and their frequency use, criteria they take into account to grade students' performances, and cognitive levels they consider while assessing student learning. Identification of difficulties that physics teachers have related to performancebased assessment was also the aim of this research. Survey research design was carried out. Participants were the physics teachers working in 61 high schools in the Anatolian side of Istanbul. Some of the conclusions are as follows: Physics teachers do not only consider where their students are according to performance goals but also value students' affective domain such as effort and attitude in order to give grades to their students. While physics teachers use traditional methods such as exam more often, they also implement performance assessment and portfolio. Physics teachers have various difficulties related to their qualifications, curriculum and university entrance exam in preparing, implementing, and evaluating performance-based assessment methods.