Patients with hypermobility syndrome (HS) and Ehlers-Danlos syndrome (EDS) were investigated by means of in vivo near- infrared Fourier-transform Raman spectroscopy. HS is a benign and common condition (up to 5 percent of the population of the Western World). EDS is a rare, inherited connective tissue disease characterized by joint hypermobility, skin hyperextensibility, and other, occasionally serious, organ changes. EDS and HS may be related disorders. We investigated 13 patients with HS, 8 patients with EDS, and 24 healthy volunteers by means of in vivo Raman spectroscopy. The patients were classified according to Beighton and Holzberg et al. No difference in age between the three groups was found (HS 41 (33-49), EDS 36 (25-47), controls 37 (31-42); mean, 95% confidence intervals, respectively). Spectral differences were found in the intensity of the amide-III bands around 1245 and 1270 cm-1 in HS and EDS compared with healthy skin (Kruskal-Wallis, p equals 0,02 for intensity ratios (I1245/I1270) between the investigated groups). To elucidate the character of the alterations in the amide-III bands a curve fitting procedure was applied. In conclusion, Raman spectroscopy may aid in the diagnosis of HS and EDS. Moreover the technique may be useful for analyzing the molecular changes occurring in these syndromes.