Human gait is a complex cyclic spatio-temporally movement that requires human joints coordination and involves several biomechanical structures. Some neurological and musculoskeletal pathologies might cause motion disorders and gait impairments, which play an important role for the quality of life and for the independence in performing daily activities. Several researches dealt with the objective assessment and biomechanical description of human gait characteristics, such as symmetry, variability and smoothness. Previous studies proposed different methods and approaches for the investigation of gait symmetry. Despite the several symmetry indexes validated in physiological gait, some challenges are still opened for the identification of robust and suitable methodology in pathological patterns.