  We study spin 1/2 isoscalar and isovector candidates in both parity channels
for the recently discovered \Theta^+(1540) pentaquark particle in quenched
lattice QCD. Our analysis takes into account all possible uncertainties, such
as statistical, finite size and quenching errors when performing the chiral and
continuum extrapolations and we have indications that our signal is separated
from scattering states. The lowest mass that we find in the I^P=0^- channel is
in complete agreement with the experimental value of the \Theta^+ mass. On the
other hand, the lowest mass state in the opposite parity I^P=0^+ channel is
much higher. Our findings suggests that the parity of the \Theta^+ is negative.
