  We present new fast numerical simulations of cosmic microwave background and
large scale structure in the case in which the cosmological dark matter is made
entirely or partly of mirror matter. We consider scalar adiabatic primordial
perturbations at linear scales in a flat Universe. The speed of the simulations
allows us for the first time to use Markov Chain Monte Carlo analyses to
constrain the mirror parameters. A Universe with pure mirror matter can fit
very well the observations, equivalently to the case of an admixture with cold
dark matter. In both cases, the analyses show a clear indication of the
presence of a consistent amount of mirror dark matter, $0.06 \lesssim
\Omega_{\rm mirror} h^2 \lesssim 0.12$.
