PROS1 and sickle cell disease: Patients at risk of thrombosis had a significant decrease in protein S (76.6% vs. 50% [<i>p</i> < 0.001]); the decrease in the latter was identified as a predictive factor of thrombotic risk during sickle cell disease (aOR = 1.5 [1.1; 5.2]; <i>p</i> = 0.04).<h4>Conclusion</h4>This study reports a significant frequency of thrombotic risk in the sickle cell population characterized by a decrease in physiological coagulation inhibitors.