The purpose of this paper is to show how important "monitoring" is as metacognitive skills in solving physics problems in the field mechanics. Based on test scores, twenty one students were divided into two groups: more successful (MS) and less successful (LS) problem solvers. Students were allowed to think-aloud while they worked on their problems. Each of the students was videotaped, and interviewed right after the task. A schema was used to grade the written answers. As a conclusion "monitoring" appeared as a very important metacognitive skill leading to successfully solving problems in mechanics. [Funding for this research was provided by the Ministry of Education (MOE), Malaysia and Universiti Teknologi Malaysia (UTM) through Grant Vote No R.J130000.7831.4F427.]