A process for preparing an aqueous styrene-butadiene polymer dispersion by free-radical aqueous emulsion polymerization of a monomer mixture M comprising styrene, butadiene, and if desired up to 30% by weight, based on 100% by weight of monomers, of ethylenically unsaturated comonomers other than styrene and butadiene; in a polymerization vessel by a monomer feed technique in the presence of a regulator system containing, based on 100% by weight of monomers, from 0.02 to 0.5% by weight of at least one hydrocarbon HC having from 6 to 20 carbon atoms, selected from compounds which on abstraction of a hydrogen atom form a pentadienyl radical or 1-phenylallyl radical, and .alpha.-methylstyrene dimer, and from 0.3 to 2% by weight of an organic compound S containing at least one SH group wherein at least 30%, preferably at least 50%, in particular at least 80%, and with particular preference the entirety (or >95%) of hydrocarbon HC is included in the initial charge to the polymerization vessel.