  In 60 inverse-pb of data taken on the psi(3770) resonance with the CLEO-c
detector, we find 8 D+ -> mu+ nu decay candidates that are mostly signal,
containing only 1 estimated background. Using this statistically compelling
sample, we measure a value of B(D+ -> mu+ nu) = (3.5 +/- 1.4 +/- 0.6) x10^(-4),
and determine fD+=(202 +/- 41 +/-17) MeV.
