We have conducted a thorough literature review to evaluate the relative value of the hematologic criterion in making a diagnosis of systemic lupus erythematosus (SLE), its clinical relevance, and its prognostic significance. In the updated 1982 ACR criteria, the presence of one or more of the four elements: 1) hemolytic anemia (with reticulocytosis); 2) leukopenia (<4000/mL on two or more occasions); 3) lymphopenia (<1500/mL on two or more occasions); or 4) thrombocytopenia (<100 000/mL in the absence of offending drugs) is now considered as a single hematologic disorder. The sensitivity and specificity of the individual elements of the hematologic criterion range from 18 to 46% and 89 to 99%, respectively. The accuracy of the hematologic criterion requires proper interpretation. For example, many studies reported the presence of anemia that was not clearly defined and likely included anemia from etiologies other than hemolytic anemia, thereby causing an overestimation of the prevalence. In addition, medications such as corticosteroids and cytotoxic agents, and viral infections, can also contribute to a reduction in lymphocyte count. Despite these limitations, the SLICC committee recommends no change in the elements of the hematologic criterion when this criterion is properly interpreted and other causes of cytopenia are excluded.