The dimensionally regularized master planar double box Feynman diagram with four massive and three massless lines, powers of propagators equal to one, all four legs on the mass shell, i.e., with p? = 1112, i = 1, 2, 3, 4, is analytically evaluated for general values of m(2) and the Mandelstam variables s and t. An explicit result is expressed in terms of polylogarithms, up to the third order, depending on special combinations of m(2), s and t. (C) 2002 Published by Elsevier Science B.V.