Background <p>Type 2 diabetes mellitus (T2DM) leads to upper extremity problems and cognitive dysfunction. This could affect the dual-task performance of individuals with T2DM.</p> Objective <p>This study was designed to examine the effect of T2DM on dual-task conditions, including upper extremity performance.</p> Methods <p>The study group (SG) consisted of 38 individuals with T2DM, and the control group (CG) consisted of 31 nondiabetic individuals. The participants’ single motor task performance was assessed using the “placing test” and “turning test” of the Minnesota Manual Dexterity Test (MMDT). As a cognitive task, participants were asked to say the names of men, women, cities, fruits, and animals in any letter of the alphabet. To assess dual-task performance, they were asked to perform the cognitive task during the “turning test” of the MMDT. The duration of tests, dual-task cost, and number of verbal errors were recorded.</p> Results <p>The SG had lower single-task placing and turning and dual-task performance than the CG (<i>p</i> &lt; 0.05). Although dual-task cost was similar between the groups, the number of verbal errors during the test was higher in the SG (<i>p</i> &lt; 0.05).</p> Conclusion <p>To our knowledge, this is the first study to examine the upper extremity performance of T2DM in dual-task conditions. The results of the study revealed that T2DM negatively affects both upper extremity motor performance and dual-task performance.</p> Trial registration <p>The study protocol was registered at clinicaltrials.gov (ID: NCT05127291, Initial Release Date: 11/09/2021).</p>