This paper introduces a simple, quantitative assessment tool to follow up the recovery of gait. Today, micro-electro-mechanical systems (MEMS) technology provides with small, simple, low-power consuming and easy to don and doff sensors. In our approach we have selected an accelerometer and introduced a new quantity that characterizes the gait pattern in the frequency domain, we term it Gait Spectral Index (GSI). GSI allows assessing gait quality and closely relates to the speed and cadence of gait (dynamics). We have tested the GSI approach to quantify the quality of the gait of healthy young and elderly, and poststroke hemiplegic individuals. We investigated the repeatability and coherence of GSI in healthy individuals (young and elderly) and contrasted this to the post-stroke hemiplegic individuals. We found that high correlation of the GSI with conventional gait parameters. This suggests that GSI, which needs only data from one accelerometer, could be an objective quantitative measure of the quality of the walking thereby a simple yet reliable measure of the recovery of function during neuronrehabilitation.