The three-dimensional shape of the back of 60 patients attending a spinal deformity clinic was measured using ISIS2, a non-commercial surface topography system using digital photography and structured light. Wire-frame and contour plots were displayed, presenting quantitative information and providing a useful pictorial representation of the whole back. A numerical parameter representing the height of the rib hump was also recorded. Repeat measurements, with the patient walking around the room between photographs were carried out. The mean difference between the pairs of measurements was -0.08 mm (sd 4.18 mm) and the 95% tolerance limits were -9.82 mm to 9.66 mm. Changes of greater than +/-10 mm are therefore necessary as indicative of clinical change.