Human CD1 group I molecules CD1a, b, and c are expressed on antigen-presenting cells, notably dendritic cells, and implicated in glycolipids presentation to T lymphocytes. Expression of CD1 on monocytes is a hallmark of their activation. Because monocyte activation has been reported during steady state disease in sickle cell anemia (SCA) patients, we have analyzed CD1 expression on monocytes from 45 SCA patients originating from Africa and 27 healthy control subjects. CD1 expression was detected on monocytes in the majority of SCA patients (75%), whereas it was not observed in the vast majority of the control group (70.4%). CD1b and CD1c were highly expressed in Sbeta thalassemia patients and CD1a expression was predominant in SDPunjab patients. This expression of the CD1 molecules is correlated with an increased expression of the major histocompatibility complex class II invariant chain (CD74). Finally, we have observed that the majority of SCA patients (68%) express only two or one CD1 isoforms. This study demonstrates the particular phenotype of SCA monocytes intermediate between normal resting and activated monocytes, a phenotype that could have consequences on regulation of the infection outcome.