  Ising model without external field on an infinite Lorentzian triangulation
sampled from the uniform distribution is considered. We prove uniqueness of the
Gibbs measure in the high temperature region and coexistence of at least two
Gibbs measures at low temperature. The proofs are based on the disagreement
percolation method and on a variant of Peierls method. The critical temperature
is shown to be constant a.s.
