Although universal newborn screening can reliably identify all infants with sickle cell hemoglobinopathies, the initial screening result must not be considered the definitive diagnosis. We describe 23 infants whose screening phenotype was FS or FC but whose true phenotype included hemoglobin A, establishing a definitive diagnosis of hemoglobin S or hemoglobin C in combination with beta(+)-thalassemia. Higher than expected hemoglobin concentrations or lower than expected mean erythrocyte volumes should suggest concurrent beta(+)-thalassemia.