The performance of the muon identification in LHCb is extracted from data using muons and hadrons produced in J/psi->mumu, Lambda->ppi and D^{star}->pi D0(Kpi) decays. The muon identification procedure is based on the pattern of hits in the muon cham
bers. A momentum dependent binary requirement is used to reduce the probability of hadrons to be misidentified as muons to the level of 1%, keeping the muon efficiency in the range of 95-98%. As further refinement, a likelihood is built for the muon and non-muon hypotheses. Adding a requirement on this likelihood that provides a total muon efficiency at the level of 93%, the hadron misidentification rates are below 0.6%.
