  We consider Higgs boson pair production via gluon fusion in hadronic
collisions. We report the calculation of the transverse-momentum ($q_T$)
distribution of the Higgs boson pair with top-quark mass ($M_t$) effects fully
taken into account. At small values of $q_T$ we resum the
logarithmically-enhanced perturbative QCD contributions up to next-to-leading
logarithmic (NLL) accuracy. At intermediate and large values of $q_T$ we
consistently combine resummation with the ${\cal O}(\alpha_S^3)$ fixed-order
results. After integration over $q_T$, we recover the next-to-leading order
(NLO) result for the inclusive cross section with full dependence on $M_t$. We
present illustrative numerical results at LHC energies, together with an
estimate of the corresponding perturbative uncertainties, and we study the
impact of the top-quark mass effects.
