  We report on the extraction of $\sin^2\theta^{\rm lept}_{\rm eff}(M_Z)$ and
an indirect measurement of the mass of the W boson from the forward-backward
asymmetry of dilepton events in the $Z$ boson mass region at the Tevatron. The
data samples of $e^+e^-$ and $\mu^+\mu^-$ events collected by the CDF detector
correspond to the full 9.4 fb$^{-1}$ run II sample and yield an effective
electroweak mixing angle $\sin^2\theta^{\rm lept}_{\rm eff}(M_Z) = 0.23222 \pm
0.00046$. The corresponding result reported by the D0 collaboration with the
full 9.4 fb$^{-1}$ $e^+e-$ sample is $\sin^2\theta^{\rm lept}_{\rm eff}(M_Z) =
0.23146 \pm 0.00047$. The CDF collaboration also extracts the on-shell
electroweak mixing angle $ \sin^2 \theta_W = 0.22401 \pm 0.00044$ which
corresponds to an indirect measurement of the W boson mass $M_W ({\rm
indirect}) = 80.327 \pm 0.023 \;{\rm GeV}$. The quoted uncertainties include
both statistical and systematic contributions.
