We report on a search for the flavor-changing neutral current decay D(0)-->mu(+)mu(-) in p (p) over bar collisions at roots=1.96 TeV using 65 pb(-1) of data collected by the CDF II experiment at the Fermilab Tevatron Collider. A displaced-track trigger selects long-lived D(0) candidates in the D(0)-->mu(+)mu(-) search channel, the kinematically similar D(0)-->pi(+)pi(-) channel used for normalization, the Cabibbo-favored D(0)-->K(-)pi(+) channel used to optimize the selection criteria in an unbiased manner, and their charge conjugates. Finding no signal events in the D(0)-->mu(+)mu(-) search window, we set an upper limit on the branching fraction B(D(0)-->mu(+)mu(-))less than or equal to2.5x10(-6) (3.3x10(-6)) at the 90% (95%) confidence level.
