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Aims. To determine the solar transition region and coronal radius at EUVwavelengths and its time evolution during Solar Cycle XXIII.  Methods. We use daily 30.4 and 17.1 nm images obtained by the ExtremeUltraviolet Imager (EIT) aboard the SoHO satellite and derive the solar radiusby fitting a circle to the limb brightness ring.  Results. The weighted mean of the temporal series gives (967''.56 +/- 0''.04)and (969''.54 +/- 0''.02) at 30.4 and 17.1 nm respectively. No significantcorrelation was found with the solar cycle at any of the two wavelengths.  Conclusions. Since the temperature formation of the 30.4 nm line is between(60 - 80) 10^3 K (Transition Region), the obtained result is bigger than thatderived from present atmospheric models. On the contrary this height iscompatible with radio models.

The Solar Radius in the EUV during the Cycle XXIII