In 1817 James Parkinson described in his Essay on the Shaking Palsy that impaired gait is one of the most important symptoms in Parkinson’s disease (PD): "Walking becomes a task which cannot be performed without considerable attention. The legs are not raised to that height, or with that promptitude which the will directs,...". Gait disorders still play an important role in PD since the diagnosis, the staging of the disease level, and also the assessment of therapeutic outcomes are based mainly on the rating of movement impairments. The state-of-the-art scores and scales to rate PD are based solely on subjective assessment of movement disorder specialists. A more objective rating of disease related impairments is therefore an urgent need to support clinical decision making. In this thesis the development of a mobile and unobtrusive system to rate gait impairments with wearable sensors is described. An inertial measurement system was used to provide standard gait parameters and a scoring that rates PD related gait impairments. This system supplies physicians and therapists of movement disorders with objective and complementary data and consequently improves clinical decision making.