Lateralization of paw preference in laboratory mice in a single-paw reaching task has been used as a model system for left- and right-hand usage. Given a set number of paw reaches for food from a centrally placed food tube, an individual mouse will exhibit a reliable number of left and right paw reaches. Within any single inbred strain, there are approximately equal numbers of left-pawed and right-pawed mice. Nevertheless, significant strain differences have been reported for the degree of lateralization of paw preference. We report here a systematic survey of paw preference in 12 inbred strains of the mouse in which the degree of lateralization falls into two groups of weakly lateralized and highly lateralized paw preference. The genetic inference is that a single major gene may control some function, and alternate alleles at this locus are expressed as weakly and highly lateralized paw preference. Reciprocal crosses indicate the trait is additive with no maternal or X-linked effects. The direction of paw preference has previously appeared to be genetically neutral, but in some strains there is evidence of significant deviation of the numbers of mice to the left and right of equal paw usage, independent of degree of lateralization, and this suggests that direction of left-right paw usage may be a separate genetic trait in the mouse model.