  In this paper we prove two results concerning the classification of Siegel
modular threefolds. Let A_{1,d}(n) be the moduli space of abelian surfaces with
a (1,d)-polarization and a full level-n structure and let A_{1,d}^{lev}(n) be
the space where one has fixed an additional canonical level structure. We prove
that A_{1,d}(n) is of general type if (d,n)=1 and n ist at least 4. This is the
best possible result which one can prove for all d simultaneously. Let p be an
odd prime and assume that (p,n)=1. Then we prove that the Voronoi
compactification of A_{1,p}^{lev}(n) is smooth and has ample canonical bundle
if and only if n is greater than or equal to 5.
