Background:There is no clear information on the efficacy of corticosteroids, and splints in the treatment of patients with diabetes mellitus (DM). The aim of this study was to compare the outcomes of isolated corticosteroid injection therapy with splint treatment with corticosteroid injection in patients with and without DM.Methods:84 diabetics, and 84 healthy patients with a diagnosis of de Quervain's tenosynovitis were included in our study. The patients were randomly distributed into four subgroups with and without DM. Groups 1 and group 2 consisted of diabetic patients, while group 3 and group 4 consisted of healthy patients. Corticosteroid injections were administered to groups 1 and 3, and corticosteroid injection and splint treatment were administered to groups 2 and 4.Results:There was no significant difference in terms of age, gender, dominant/non-dominant hand, pre-treatment Quick Disabilities of the Arm, Shoulder and Hand score and visual analog scale scores score between the four groups. Quick Disabilities of the Arm, Shoulder and Hand and visual analog scale scores in the four groups were found to be significantly better than pre-treatment at the 12th month. Finkelstein test results were positive in 37.5% of the patients in the first group, 35% of the patients in the second group, 20% of the patients in the third group and 9.5% of the patients in the fourth group. Groups 1 and 2 and, groups 3 and 4 were compared to evaluate the effect of the splint. While forearm-based thumb splint affected the results positively in healthy individuals, it was determined that it had no effect on the results in diabetic patients.Conclusion:Although corticosteroid treatment is effective in the treatment of de Quervain's tenosynovitis in healthy and diabetic individuals, the results are worse in diabetic patients than in healthy patients. In addition, the use of splint with corticosteroid injection in healthy individuals positively affects the results, while it does not affect the results in diabetic patients.