The "intrinsic" surface tension of liquid He II, arising from the structural energy of the free surface, is calculated on the basis of Gross and Pitaevski's imperfect-gas model. The resulting expression, when supplemented by the contribution arising from the presence of quantized surface modes of vibration, gives a value of 0.28 erg cm-2 for the surface tension of liquid helium in the limit T --> 0°K. This value compares well with the experimental estimate of 0.37 erg cm-2. It is also demonstrated that the so-called boundary effects, which arise from a better enumeration of the density of states in a bounded statistical system, do not make a significant contribution to the temperature dependence of the surface tension. The dominant contribution is again the one due to the quantized surface modes.