A 9-month-old male infant was evaluated for sudden onset of paroxysmal episodes of forced, conjugate upward eye deviation. Extensive in-hospital evaluation including electrophysiology and neuroimaging studies were reassuring against seizures or a structural abnormality. Given the clinical presentation of sudden onset intermittent upward eye deviations, downbeating saccades, associated ataxia, and typical development, a clinical diagnosis of paroxysmal tonic upgaze (PTU) with ataxia was made. Targeted genetic testing of CACNA1A was performed, which revealed a variant of undetermined significance, which was later classified as a de novo pathogenic variant after protein modeling and parental testing performed. Off-label use of oral acetazolamide was prescribed, which led to dose-responsive decrease in the frequency and intensity of eye movement episodes. After 6 months of episode freedom at 2 years of age, acetazolamide was discontinued without return of episodes. Neurodevelopmental assessments revealed continued typical development. This case is presented to describe the diagnostic formulation, etiologic evaluation, and symptomatic treatment of CACNA1A-related PTU with ataxia.