In the MACRO experiment the flux of atmospheric muon neutrinos has been studied through the detection of upward-going muons generated in the rock below the detector and also through neutrino interactions inside the apparatus. Several topologies of neutrino events have been detected, which correspond to different neutrino parent energies. The measured flux in the different data sets shows a deficit with respect to the Monte Carlo predictions. Moreover, the upward-throughgoing muon sample (median neutrino energy ∼ 50 GeV) also shows a distortion in the angular distribution shape. Interpreted in terms of neutrino oscillation, these results favor a vμ into vτ oscillation scenario, while the νμ into νsterile channel is disfavared at 99% C.L