Objective Recently the fast progress in the development of systems attending the three-dimensional gait evaluation is being observed. One of the indexes used to the analysis is Gillette Gait Index (GGI), complying 16 clinically meaningful kinematic and three-dimensional parameters. Methods The study was conducted with application of the three-dimensional system of gait analysis BTS Smart and carried by the team of pediatric neurologists, physiotherapists and engineers. Spatial-time parameters of gait and courses of angles of joint of lower limbs were determined on the basis of conducted research. Those parameters were used in estimation of Gillette Gait Index. The analyzed group consisted of ten CP patients treated with botulin toxin (three children with hemiparesis, seven with diparesis), intensively rehabilitated after the botulin treatment. The data were compared to four patients put on rehabilitation without the botulin treatment. The patients treated with botulin were evaluated three times: before the botulin administration, then three and six months after it. In the other patients' group the evaluation was conducted three months after rehabilitation start. The results of gait evaluation were compared to the gait pattern of the healthy children; the normal values were worked out by the authors. Results After the botulin treatment and rehabilitation the increase of the gait speed and frequency of steps were observed; the GGI decreased both after three and six months of observation. The locomotive function of the patients' improved in 70% of them. Conclusion The authors regard the results presented above as the pilot-study; the evaluation of the larger groups of children with cerebral palsy is conducted. In the authors' opinion the objective method of CP children gait evaluation may be the helpful tool for clinicians to optimize the way of CP children treatment. Study realized as a part of the DEC-2011/01/B/NZ7/02695 project, financed by National Science Centre.