Diabetes is known to cause an array of central and peripheral neurological conditions. Among the neuropathic complications associated with diabetes are distal symmetrical polyneuropathy, amyotrophy, polyradiculopathy, autonomic neuropathy, and cranial mononeuropathies. Notably, brachial plexopathy has not been documented as a complication of diabetes. A 50-year-old man with a history of diabetes mellitus presented with severe pain and progressive weakness in his right upper limb. Laboratory investigations, immunopathological analyses, and cerebrospinal fluid examination yielded normal results. The electrodiagnosis and imaging studies were consistent with bilateral brachial plexus neuritis. This unique presentation does not align with the rare diabetic polyradiculopathy of the upper limbs commonly linked to diabetic amyotrophy. The association between diabetes mellitus and brachial plexopathy is uncommon, indicating a possible occurrence of a rare subtype within diabetic neuropathies.