Imagery is the most widely used psychological skill in elite sport. Measuring imagery ability is important for researchers and practitioners in sport psychology. Although a variety of tests and questionnaires currently exist, as yet no multi-modal, multi-dimensional, sport specific measure has been fully validated. The purpose of this paper is to describe the convergent and discriminant validation of an assessment tool for use in imagery training programs, the Sport Imagery Ability Measure (SIAM). The Revised SIAM is a 48 item self-report measure that uses four sport related scenes to examine the imagery dimensions of vividness, control, duration, ease, and speed of generation; imagery in the visual, auditory, olfactory, gustatory, tactile, and kinesthetic senses; and the imagery of the sensation of emotion. Individual subscale scores of the SIAM were correlated with subscale and total scores of the following measures: Shortened Form of the Questionnaire on Mental Imagery (SQMI); Vividness of Movement Imagery Questionnaire-II (VMIQ); Gordon Test of Visual Imagery Control (GTVIC); and the similarities and spatial subtests of the Multidimensional Aptitude Battery (MAB). Participants (N = 436) from high schools, university physical education courses, and elite sports groups completed the six measures over two sessions. Small to moderate correlations (.27 to .48) were found for the SIAM control, vividness, visual, and kinesthetic subscales with a number of the related dimension and modality variables of the other imagery measures, providing support for the convergent validity of these subscales of the SIAM. Very low to small correlations (.01 to .30) were found for the cognitive ability measures and unrelated dimension and modality variables of the other imagery measures, with the SIAM subscales, supporting discriminant validity. Implications of this research in substantiating the suggested dimensional and modality structure of this new measure are discussed.