Recently, 1997, Tanner and co-workers provided a new scale converting TW-RUS standard maturity scores to skeletal age for European North American youths (US90). The aim of the present study was to test if the accuracy of TW-RUS bone age assessments in the Italian population could be improved by evaluating the estimates obtained with this new scale in comparison with other standards (UK60: original British series, B70: Belgian series and S80: Spanish series). 1,831 hand-wrist radiographs (Italian healthy subjects aged from 8 to 16.8 years) were evaluated. The US90 reference values are resulted the most suitable TW-RUS standards. Therefore, it seems useful to update the reference values of TW-RUS SMS in Italian youths, using this new scale.