['The aim of this study is to assess biological prognostic factors at the onset of vaso-occlusive crisis (VOC) in adults with sickle cell disease (SCD).', 'A monocentric prospective study including all patients admitted for VOC in a reference center for SCD was utilized. We used multivariate logistic regression to find independent predictors of severe evolution, defined by death or a worsening clinical state indicating transfusion or transfer to the intensive care unit.', 'Eighty eight patients were included, 63% were women, median age of 23 years, and 90% of patients were homozygous SCD, 10% compound heterozygous. VOC became severe in 17 patients. Patients with severe VOC were more frequently males, who also had higher white blood cell (WBC) count, procalcitonin (PCT), and lactate dehydrogenase (LDH) levels. LDH level was the best predictor of the outcome; WBC and PCT had no significant added predictive values when coupled with LDH in multivariable models, even in patients with fever or acute chest syndrome. Severe evolution always occurred when LDH levels were over 4 times the upper limit of the normal range at admission and never occurred when LDH levels were within the normal range.'] Is high lactate dehydrogenase levels at admission for painful vaso-occlusive crisis associated with severe outcome in adult SCD patients?