Many diseases, different nutritional, metabolic and hormonal changes, ageing and drugs can alter cognitive functions. Anemia via cerebral hypoxia and other possible mechanisms has been suggested to have a great influence on cognition. Iron deficiency anemia, the most common form of anemia, has been suggested to result in cognitive deterioration and alteration of neurological functions. Previous studies resulted in significant discrepancies considering correlation between anemia and cognitive achievement mainly because different or not sensitive enough tests used to measure cognition. We suggest a significant influence of iron deficiency anemia on dynamic properties and functional features of the central nervous system activity. Cognitive achievement is strongly related to hemoglobin level and could be expected in all patients. Higher hemoglobin level results in better CNS function. As a first step in confirming or refuting our hypotheses we suggest standardization of the method used to measure cognition, such as a very sensitive apparatus like Complex reactiometer Drenovac (CRD).