Little is known about the pharmacokinetics of hydroxyurea in patients with sickle cell disease (SCD). Our aims were to evaluate bioequivalence between standard hydroxyurea capsules and a new formulation of 1,000 mg coated breakable tablets in adults and to compare pharmacokinetic parameters in adults and children with SCD. Fifteen adults received hydroxyurea capsules and tablets in a randomized cross-over study. Eleven children received hydroxyurea tablets. The results showed bioequivalence between capsules and tablets in adults. Pharmacokinetic parameters were not significantly different between adults and children. Considerable inter-individual variability was noted.