Reported was an explanatory conceptual model for pathological left-handedness (PLH) and related hypotheses, some of which could not be tested empirically due to lack of information. The model was reported to provide an explanation for the relationship between handedness and specific learning disability, and handedness and cerebral dominance for speech. The model stated that the incidence of PLH will increase as a function of early brain injury. It was demonstrated that the ratio of PLH to pathological right-handedness was independent of the magnitude of the value of manual switch. The two hypotheses which could not be tested involved the manual switch value and the relationship of the incidence of familial sinistrality, in pathological left-handedness groups, to that in normal right-handed control groups. Hypotheses said to be tentatively proven focused on the probability of brain lesion in the left hemisphere if the subject is left-handed and is retarded or epileptic, the probability that such a person is a pathological left-hander, the incidence of manifest left-handedness in brain-injured populations with perinatal or early post-natal injury, and the incidence of pathological left-handedness in comparison to that of natural left-handedness. (CB)