Typical physics textbook problems often include supportive diagrams that visualize the physical situation although the potential benefits of providing such diagrams is not yet fully established. We used eye tracking to explore the role of supportive diagrams in problem solving. Including a supportive diagram with the text of the problem improved students’ percentage of correct answer in one of the six problems used in the study. Eye-tracking data showed that students typically spent less time on the text of the problem if they were presented with a diagram, but the total viewing time did not change. When a diagram was presented students split their attention between the diagram and the text without speeding up problem solving. Cognitive load theory and dual coding theory suggest that giving information in two formats (verbal and visual) might reduce extraneous cognitive load and leave more cognitive resources available for further steps in problem solving. However, this does not necessarily lead to a higher percentage of correct answers to the problem, because supportive diagrams influence only one step of the complex process of problem solving. In addition to the role of diagrams, we evaluated different eye-tracking measures as measures of visual attention during physics problem solving. It seems that the fixation duration is rather constant, and not always sensitive to the manipulation in the task. On the other hand, dwell time and the number of fixations show more variability across problems and participants, so they seem to be appropriate measures of the visual attention. Since dwell time and fixation number are dependent measures, and they show a similar pattern of responses, in most cases it seems sufficient to report only one of them.