We examined the frequency of left-handedness, various immune disorders, and comparison disorders in 87 dyslexics and 86 nondyslexics from 14 extended dyslexic families. These families were participants in our genetic linkage studies of dyslexia, which found linkage to chromosome 15 in some families but not others. In the present study, we found a significant elevation of both autoimmune and allergic disorders in the dyslexics only, but no elevation in mixed- or left-handedness in either group. Moreover, the frequency of immune disorders was not higher in the mixed- or left-handed subjects. There was also no elevation in the comparison disorders, which argues against an overreporting bias. The elevation of immune disorders did not vary with linkage status, arguing against a common cause for dyslexia and immune disorders. These findings are discussed in light of Geschwind's hypothesis of a testosterone-mediated association within families between left-handedness, immune disorders, and dyslexia.