  We measure the asymmetry in the charge-weighted rapidity of the lepton in
semileptonic ttbar decays recorded with the CDF II detector using the full
Tevatron Run II sample, corresponding to an integrated luminosity of 9.4/fb. A
parametrization of the asymmetry as a function of the charge-weighted rapidity
is used to correct for the finite acceptance of the detector and recover the
production-level asymmetry. The result of afb(lep) = 0.094 +0.032 -0.029 is to
be compared to the standard model next-to-leading-order prediction of afb(lep)
= 0.038 +-0.003.
