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 study the model close to criticality in both phases. Great care is taken to control systematic errors due to finite size effects and correction to scaling terms. We obtain 0305-4470/30/14/010/img5, 0305-4470/30/14/010/img6 and 0305-4470/30/14/010/img7. Our results are compatible with those obtained by field theoretic methods applied to the 0305-4470/30/14/010/img8 theory and high- and low-temperature series expansions of the Ising model. The mismatch with a previous Monte Carlo study by Ruge et al remains to be understood.