The carpal tunnel syndrome (CTS) occurs frequently in patients with diabetes mellitus. The prevalence of CTS is higher in diabetic patients with peripheral polyneuropathy compared to patients with diabetes, who do not have diabetes-related late complications (30% vs. 14%). Moreover, CTS seems to be a risk factor for later manifestation of diabetes mellitus, as patients with newly diagnosed diabetes showed CTS manifestation 1.4-fold more often than the age-matched reference population. This paper describes the diagnostics, differential diagnostics and particularities in the therapy of patients with both CTS and diabetes. In case of oral or local application of corticoids, the persistent elevation of blood glucose levels has to be taken into account with potential need for intensification of diabetes therapy. In case of progression of the CTS, surgery is indicated.