  We report on computations of the cohomology of GL_2(O_D) and SL_2(O_D), where
D<0 is a fundamental discriminant. These computations go well beyond earlier
results of Vogtmann and Scheutzow. We use the technique of homology of Voronoi
complexes, and our computations recover the integral cohomology away from the
primes 2, 3. We observed exponential growth in the torsion subgroup of H^2 as
$D$ increases, and compared our data to bounds of Rohlfs.
