A measurement of the rate for the "wrong-sign" decay D-0 -> K+pi(-)pi(+)pi(-) relative to that for the "right-sign" decay D-0 -> K-pi(+)pi(+)pi(-) is presented. Using 791 fb(-1) of data collected with the Belle detector, we obtain a branching fraction ratio of R-WS = [0.324 +/- 0.008(stat) +/- 0.007(sys)]%. Multiplying this ratio by the world average value for the branching fraction B(D-0 -> K-pi(+)pi(+)pi(-)) gives a branching fraction B(D-0 -> K+pi(-)pi(+)pi(-)) = (2.61 +/- 0.06(-0.008)(+0.09)) x 10(-4).