The aim of this study was to analyze the changes in the standing center of pressure (COP) in a hemiplegic adult population at the beginning and the end of in-patient rehabilitation. The trajectory of the COP was recorded on a force platform and was analyzed in terms of the frequency spectra of the center of gravity (COG), and the frequency spectra of the COP minus COG, a derived measure of neuromuscular stiffness. The study population consisted of eight hemiplegic subjects, median age of 53.5 years (range 27-79 years). The median interval between stroke and the first series of measures was 31 days (range 4-127) and the median interval between the two measures was 47.5 days (range 12-92). All the subjects were treated in an inpatient setting in a Neurorehabilitation Center. Our results showed that following rehabilitation, there was a reduction in the amplitude of the medio-lateral frequency spectra of the COP from a median of 5.651 mm (range 3.13-14.05) at the first measurement to 4.408 mm (range 2.40-8.58) at the second measurement. These changes were significant (p<0.05). Significant changes were also observed in the measure of COP minus COG, from 1.324 mm (range 0.92-2.63) on the first measure to 0.917 mm (range 0.46-1.53) on the second measure. In conclusion, the medio-lateral COP trajectory of hemiplegic subjects significantly improved during rehabilitation. We hypothesized that a major component of this improvement was the decrease in neuromuscular stiffness of the adductor and abductor muscles of the hips.