Background: It is generally accepted that the initial treatment for trigger finger is injection of corticosteroid into the flexor tendon sheath. In this study, the efficacy of corticosteroid injections for the treatment of trigger finger in patients with diabetes mellitus was evaluated in a prospective, randomized, controlled, double-blinded fashion and the efficacy in nondiabetic patients was evaluated in a prospective, unblinded fashion. Methods: Thirty diabetic patients (thirty-five digits) and twenty-nine nondiabetic patients (twenty-nine digits) were enrolled. The nondiabetic patients were given corticosteroid injections in an unblinded manner. The cohort with diabetes was randomized into a corticosteroid group (twenty digits) or a placebo group (fifteen digits). Both of these groups were double-blinded. Additional injections, surgical intervention, and recurrent symptoms of trigger finger were recorded. Treatment success was defined as complete or nearly complete resolution of trigger finger symptoms such that surgical intervention was not required. Results: After one or two injections, twenty-five of the twenty-nine digits in the nondiabetic group had a successful outcome compared with twelve of the nineteen in the diabetic corticosteroid group (p = 0.03) and eight of the fifteen in the diabetic placebo group (p = 0.006). With the numbers studied, no significant difference was found between the diabetic groups. Surgery was performed in three of the twenty-nine digits in the nondiabetic group compared with seven of the nineteen in the diabetic corticosteroid group and six of the fifteen in the diabetic placebo group. There was a significant difference in the prevalence of surgery between the nondiabetic group and both the diabetic corticosteroid group and the diabetic placebo group (p = 0.035 and p = 0.020, respectively). With the numbers studied, no difference was found between the diabetic groups with regard to the persistence of symptoms. Nephropathy and neuropathy were significantly associated with the need for surgery (p = 0.008 and p = 0.03, respectively). Conclusions: Corticosteroid injections were significantly more effective in the digits of nondiabetic patients than in those of diabetic patients. In patients with diabetes, corticosteroid injections did not decrease the surgery rate or improve symptom relief compared with the placebo. The use of corticosteroid injections for the treatment of trigger finger may be less effective in patients with systemic manifestations of diabetes mellitus. Level of Evidence: Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.