Thoracic kyphosis angle measurements using surface topography with ISIS2 were carried out to estimate the inherent variability in the parameter caused by natural change in the patient's stance, breathing and muscle tension. A mean kyphosis angle of 33.8° (sd 13.4°, range 6°–66°) was measured from repeat tests on 61 patients. The mean difference between the pairs of measurements was −0.02° (sd 3.18°) and the 95% tolerance limits were −7.41° to 7.38°. This variability is lower than the clinically significant change in kyphosis angle reported in the literature. Thus kyphosis angle in ISIS2 is suitable for monitoring progress in kyphotic deformities.