Hereditary spastic paraplegia (HSP) and spastic diplegia (SD) patients share a strong clinical resemblance. Thus, HSP patients are frequently misdiagnosed with a mild form of SD. Clinical gait analysis (CGA) has been highlighted as a possible tool to support the differential diagnosis of HSP and SD. Previous analysis has focused on the lower-body but not the upper-body, where numerous compensations during walking occur. The aim of this study was to compare the full-body movements of HSP and SD groups and, in particular, the movement of the upper limbs. Ten HSP and 12 SD patients were evaluated through a CGA (VICON 460 and Mx3+; ViconPeak[R], Oxford, UK) between 2008 and 2012. The kinematic parameters were computed using the ViconPeak[R] software (Plug-In-Gait). In addition, the mean amplitude of normalised (by the patient's height) arm swing was calculated. All patients were asked to walk at a self-selected speed along a 10-m walkway. The mean kinematic parameters for the two populations were analysed with Mann-Whitney comparison tests, with a significant P-value set at 0.05. The results demonstrated that HSP patients used more spine movement to compensate for lower limb movement alterations, whereas SD patients used their arms for compensation. SD patients had increased shoulder movements in the sagittal plane (Flexion/extension angle) and frontal plane (elevation angle) compared to HSP patients. These arm postures are similar to the description of the guard position that toddlers exhibit during the first weeks of walking. To increase speed, SD patients have larger arm swings in the sagittal, frontal and transversal planes. Upper-body kinematics, and more specifically arm movements and spine movements, may support the differential diagnosis of HSP and SD. (Contains 4 tables and 1 figure.)