  A search for the flavor-changing neutral-current decay $\Lambda_{c}^{+} \to
p\mu^+\mu^-$ is reported using a data set corresponding to an integrated
luminosity of $3.0\rm fb^{-1}$ collected by the LHCb collaboration. No
significant signal is observed outside of the dimuon mass regions around the
$\phi$ and $\omega$ resonances and an upper limit is placed on the branching
fraction of $\mathcal{B} (\Lambda_{c}^{+} \to p\mu^+\mu^-) < 7.7~(9.6)\times
10^{-8}~{\rm at}~90\%~(95\%)$ confidence level. A significant signal is
observed in the $\omega$ dimuon mass region for the first time.
