Abstract Background Mutations in the adenylate cyclase 5 (ADCY5) gene are associated with childhood-onset paroxysmal dyskinesia. Methods We report a new video-documented case of pediatric ADCY5-related dyskinesia with de novo ADCY5 mutation. Results A boy born to nonconsanguineous parents after an uneventful pregnancy had developmental delay and hypotonia. At the age of 7 months, he presented with paroxysmal jerky–choreic–dystonic involuntary movements in wakefulness involving limbs, trunk, and face, exacerbated by emotional stimuli. These episodes gradually worsened in duration and frequency: at the age of 2.5 years, they occurred up to six times per day, and appeared also during sleep in prolonged bouts; the boy also had basal choreoathetoid–dystonic movements, hyperactivity, paraparetic–ataxic gait, generalized hypotonia with brisk tendon reflexes, drooling, and language delay with intellectual disability. Brain magnetic resonance imaging, electroencephalogram, electromyogram, eye review, metabolic investigations, oligoclonal bands, and autoantibodies were normal. Extensive genetic testing had not let to a diagnosis, until a heterozygous de novo mutation c.1252C > T (p.Arg418Trp) was identified in the ADCY5 gene. Clonazepam had partial effectiveness. The boy walked at the age of 3.5 years. At the age of 5 years, the paroxysmal movement disorder has slightly improved. Conclusion ADCY5 mutations should be considered among the differential diagnoses of early-onset paroxysmal choreic–athetosic–myoclonic–dystonic movement disorder involving limbs, trunk, and face, in patients with global neurological impairment with hypotonia and developmental delay. Facial dyskinesias and exacerbation by drowsiness/sleep and emotional stimuli are important clues that may allow a timely recognition of the disorder and avoidance of unnecessary diagnostic investigations.