Searches for heavy Majorana neutrinos in B- decays in final states containing hadrons plus a mu(-) mu(-) pair have been performed using 0.41 fb(-1) of data collected with the LHCb detector in proton-proton collisions at a center-of-mass energy of 7 TeV. The D+ mu(-) mu(-) and D*+ mu(-) mu(-) final states can arise from the presence of virtual Majorana neutrinos of any mass. Other final states containing pi(+), D-s(+), or D-0 pi(+) can be mediated by an on-shell Majorana neutrino. No signals are found and upper limits are set on Majorana neutrino production as a function of mass, and also on the B- decay branching fractions.