A measurement of the lepton charge asymmetry in inclusive pp → WX production at $ \sqrt {s} = 7\;{\text{TeV}} $ is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 pb−1. This high precision measurement of the lepton charge asymmetry, performed in both the W → eν and W → μν channels, provides new insights into parton distribution functions.