This study investigated problem solving skills in mechanics problems that required the use of diagrams. These skills were examined in two ways. First, the study examined student problem solving skills using solution scripts from the Western Australian Tertiary Admission Examination in physics. Solution attempts by students in the 1978 and 1979 physics papers were used as an information base, to identify and classify student difficulties in selected mechanics problems. Second, student problem solving skills were further examined to detail the error types in performance on diagram analysis. A population of students attempted to solve selected problems. Their solution attempts followed four seperate methods. Each method of solution was analyzed separately. The findings of this analysis identified many points of difficulty. A further study examined in detail the errors involved in student performance on diagram analysis. Analysis of test results provided information on the initial steps and difficulties for student problem solvers using diagrams as a solution aid. The general findings of this study suggest that student inability to use diagram analysis is a major influence on the lack of mechanics problem solving competence among tertiary admission examinees. There is in this finding an implied demand for a clearer problem solving strategy, where the use of diagram analysis is appropriate. (Author/CW)