The mature mammalian nervous system alters its functional organization in a use-dependent manner. Enhanced stimulation of a body part enlarges its cortical representational zones and may change its topographic order. Little is known about the perceptual and behavioral relevance of these plastic alterations in cortical organization. We used blind Braille readers who use several fingers on each hand and who do so for many hours each day as a model to investigate this issue. Magnetic source imaging indicated that the cortical somatosensory representation of the fingers was frequently topographically disordered in these subjects; in addition, they frequently misperceived which of these fingers was being touched by a light tactile stimulus. In contrast, neither the disordered representation nor mislocalizations were observed in sighted controls. Blind non-teacher Braille readers who used only one finger for reading were not significantly different from the sighted controls. Thus, use-dependent cortical reorganization can be associated with functionally relevant changes in the perceptual and behavioral capacities of the individual.