We have determined m(W) = 79.91 +-0.39 GeV/(c**2) from an analysis of W -->
e nu and W --> mu nu data from the CDF detector in p anti-p collisions at
s**(1/2) = 1.8 TeV.  This result, together with the world average Z mass,
determines the weak mixing angle to be sin**2 theta(W) = 0.232 +- 0.008.
Bounds on the top quark mass are discussed.