Quantitative 3-D reconstruction of body surface represents a useful tool in many medical fields, such as prosthetics, plastic surgery, orthopaedics. Particularly in this last area, the analysis of back surface may give an essential improvement to the evaluation of spinal deformities and to the follow up of their progressive features. The aim of this paper is to present a new method that is able to measure with great accuracy the 3-D co-ordinates of a whatever number of sample points on the back surface, to compute and render the reconstructed surface, and to analyse quantitatively its shape. Such a method utilises an automatic image analyser (the ELITE System) joined with a suitable device scanning the surface by means of a laser beam. Starting from at least two different views of the subject, the image analyser computes in real time the 3-D co-ordinates of each sample point on the surface. A dedicated software for data processing and graphic representation completes the reconstruction of the back surface.