Using 281fb-1 of data from the Belle experiment recorded at or near the Υ(4S) resonance, we have measured the rates of the "wrong-sign" decays D0→K+π-π0 and D0→K+π-π+π- relative to those of the Cabibbo-favored decays D0→K-π+π0 and D0→K-π+π+π-. These wrong-sign decays proceed via a doubly Cabibbo-suppressed amplitude or via D0-D̄0 mixing; the latter has not yet been observed. We obtain RWS(Kππ0)=[0.229±0.015(stat)-0.009+0.013(syst)]% and RWS(K3π)=[0.320±0.018(stat)-0.013+0.018(syst)]%. The CP asymmetries are measured to be -0.006±0.053 and -0.018±0.044 for the K+π-π0 and K+π-π+π- final states, respectively. © 2005 The American Physical Society.