One hundred and seventy-four patients with De Quervain's tenosynovitis were randomized to receive a thumb Spica cast and a corticosteroid injection (1mL of 10 mg) of triamcinolone acetonide and (1mL) lidocaine, or a thumb Spica cast alone to evaluate improvement in pain and function. The primary outcomes of interest included pain on a Visual Analog Scale (VAS) and the Quick Disability of the Arm, Shoulder and Hand (QuickDASH) score. Both groups displayed significant improvements in VAS pain scores and QuickDASH scores after treatment compared to baseline scores. Between-group comparisons were not performed; however, the casting plus corticosteroid group demonstrated lower and thus, better VAS pain scores and QuickDASH scores compared to the casting only group. A larger number of patients in the casting only group reported continuous pain following treatment compared to the casting plus corticosteroid group.