Cognitive research on the number, counting, and arithmetic competencies of children with a learning disability in arithmetic (AD) is reviewed, and similarities between the associated deficits of AD children and the deficits of individuals afflicted with dyscalculia are highlighted. It is concluded that the defining features of AD and most dyscalculias are difficulties with the procedural features associated with the solving of complex arithmetic problems and difficulties in remembering basic arithmetic facts. The procedural deficits and one form of retrieval deficit appear to be associated with functioning of the prefrontal cortex, while a second form of retrieval deficit appears to be associated with the functioning of the left parieto-occipito-temporal areas and several subcortical structures. The review ends with a discussion of the potential relation between this second form of retrieval deficit and dyslexia.