Model neurons composed of hundreds of compartments are currently used for studying phenomena at the level of the single cell. Large network simulations require a simplified model of a single neuron that retains the electrotonic and synaptic integrative properties of the real cell. We introduce a method for reducing the number of compartments of neocortical pyramidal neuron models (from 400 to 8-9 compartments) through a simple collapsing method based on conserving the axial resistance rather than on the surface area of the dendritic tree. The reduced models retain the general morphology of the pyramidal cells on which they are based, allowing accurate positioning of synaptic inputs and ionic conductances on individual model cells, as well as construction of spatially accurate network models. The reduced models run significantly faster than the full models, yet faithfully reproduce their electrical responses.