There is growing consensus that the process of planning mathematics lessons is as complex as teaching them, yet there is limited research on this. This paper reports on one aspect of a project examining issues in primary teachers' mathematics planning. The results, taken from a questionnaire completed by 62 primary teachers, indicate that when planning their lessons, teachers give priority to a diverse range of aspects related to their mathematical knowledge for teaching, yet there are similarities in the challenges which they experience. Findings also suggest that team planning can support teachers overcome such challenges. Issues requiring further attention are discussed.