Present data acquired by functional neuroimaging in dyslexia suggests a diverse range of neurofunctional deficits. The range of neurobehavioral disorders that have been investigated by computed tomography (CT) and magnetic resonance imaging (MRI) technology has reflected two rather different theoretical perspectives, seldom reconciled. The modular cognitive model postulates that a circumscribed, relatively specific cognitive process is disrupted in relative isolation from other processes. Comorbidity is often considered in psychiatric nosology as a problem that threatens the accuracy and specificity of diagnosis. Subtraction methodology compares a given cognitive activation task with a control condition in an effort to isolate a particular cognitive mechanism that is impaired. Longitudinal studies are possible with fMRI and may allow data to be acquired early enough in childhood to capture the genetic heterogeneity at a time when it is less subtle and more readily demonstrable.