Fourier transform Raman (FT-Raman), attenuated total reflection/Fourier transform infrared (ATR/FT-IR) spectra and differential scanning calorimetry (DSC) measurements were performed on a biodegradable periodontal membrane, the Vicryl periodontal mesh, in order to study its in vitro and in vivo degradation mechanism and kinetics. The hydrolitic in vitro degradation was investigated in two aqueous media: a saline phosphate buffer (SPB, pH=7.4) and a 0.01 M NaOH solution. Moreover, a membrane implanted in vivo for 4 weeks for treatment of contiguous vertical bony defects, was examined. Vibrational and thermal measurements show that the Vicryl membrane presents a semicrystalline structure. It degrades faster in the NaOH solution than in the SPB and degradation occurs heterogeneously with a progressive increase in the percentage of crystallinity and shortening of the polymeric chains both in vitro and in vivo. The trends of % weight loss and IR I627/I1415 intensity ratio (identified as a marker of crystallinity) are discussed in comparison with the DSC results. The IR I627/I1415 intensity ratio and Xc% allow to determine the % weight loss undergone by the membrane degraded in vivo. The result obtained shows that the Vicryl membrane degrades faster in vivo than in vitro with the formation of oligomers which are more easily absorbed by the surrounding tissues than they are soluble in the degradation media examined.