  We present a high precision Monte Carlo study of various universal amplitude
ratios of the three dimensional Ising spin model. Using state of the art
simulation techniques we studied the model close to criticality in both phases.
Great care was taken to control systematic errors due to finite size effects
and correction to scaling terms. We obtain $C_+/C_-=4.75(3)$,
$f_{+,2nd}/f_{-,2nd}=1.95(2)$ and $u^*=14.3(1)$. Our results are compatible
with those obtained by field theoretic methods applied to the $\phi^4$ theory
and high and low temperature series expansions of the Ising model. The mismatch
with a previous Montecarlo study by Ruge et al. remains to be understood.
