We obtained the spectrum of the Sinai billiard as the zeros of a secul
ar equation, which is based on the scattering matrix of a related scat
tering problem. We show that this quantization method provides an effi
cient numerical scheme, and its implementation for the present case gi
ves a few thousands of levels without encountering any serious difficu
lty. We use the numerical data to check some approximations which are
essential for the derivation of a semiclassical quantization method ba
sed also on this scattering approach.