Many complex cells in mammalian primary visual cortex are finely tuned to binocular disparity. In the prevailing model, several binocular simple cells drive each disparity-tuned complex cell. However, some cat complex cells receive direct LGN input, and binocular simple cells are rare in macaque. In our biophysically detailed compartmental model, active dendrites of a single neuron perform the multiple simple-cell-like subunit computations that underlie both orientation and disparity tuning. The responses of our detailed model could be predicted by a simple algebraic formula closely related to an 'energy' model. Adding inhibitory synapses led to sharper, more contrast-invariant tuning curves. Thus active dendrites could contribute to binocular-disparity tuning in complex cells.