We present the first direct measurements of the pion valence-quark momentum distribution which is related to the square of the pion light-cone wave function. The measurements were carried out using data on diffractive dissociation of 500 GeV/c pi (-) into dijets from a platinum target at Fermilab experiment E791. The results show that the /q (q) over bar > light-cone asymptotic wave function describes the data well for Q(2) similar to 10 (GeV/c)(2) or more. We also measured the transverse momentum distribution of the diffractive dijets.