We present a search for the "wrong-sign" decay D0---> K+ pi (-) pi (+) pi (
-) using 9 fb(-1) of e(+)e(-) collisions on and just below the Y(4S) resona
nce. This decay can occur either through a doubly Cabibbo-buppressed proces
s or through mixing to a (D) over bar (0) followed by a Cabibbo-favored pro
cess. Our result for the time-integrated wrong-sign rate relative to the de
cay D-0-->K- pi (+) pi (-) pi (+) is (0.0041(-0.0011)(+0.0012)(stat)+/-0.00
04(syst))x(1.07 +/-0.10)(phase space). which has a statistical significance
of 3.9 standard deviations.