Monoballism secondary to a mixed hyperglycemic crisis is a rare initial symptom of new-onset diabetes, which commonly affects the elderly and Asian women having inadequate glycemic control. In hyperglycemic states, the elevated serum glucose levels raise the viscosity of the blood reducing cerebral perfusion, decreasing gamma-aminobutyric acid levels, the latter being an inhibitory neurotransmitter of thalamocortical stimuli. In this case, we report a previously healthy 41-year-old male who attended the emergency department because of an abrupt onset movement disorder of the left arm, this being compatible with monoballism. He was diagnosed with a mixed hyperglycemic crisis.