The prevalence of functional asplenia in Omani children with sickle cell disease (SCD) has not been previously defined. In this study, the authors aim to compare the natural history of splenic dysfunction in their patients to other reports. The splenic function was studied in 72 Omani patients with sickle cell disease (50 homozygous for hemoglobin S (HbS-S), 11 double heterozygotes for HbS and beta(0)-thalassemia (HbS-beta(0)-thal), 5 HbS-beta(+)-thal, 5 patients with hemoglobin S-D disease, and 1 child with hemoglobin S oman trait) aged 4.8-16 years, using (99m)Tc-labeled tin colloid scintigraphy. The study revealed 4 groups according to their colloid uptake: group I included 20 patients (28%) with normal splenic function; group II, 6 patients (8%) with mild hyposplenism; group III, 20 (28%) with severe hyposplenism; and group IV, 26 (36%) patients with functional asplenia. Overall, more than 60% of them had preserved splenic function. Except for HbS-beta(+) patients, the developmental pattern of hyposplenism was not different among the different Hb phenotypes. Factors associated with preservation of spleen function in these patients were larger splenic size (p < .01), less clinical severity (p < .05), lower MCH (p < .01), higher HbF (p < .001), and presence of alpha-thalassemia trait (p < .05).