Adult-onset Lhermitte-Duclos disease (LD), or dysplastic cerebellar gangliocytoma, is a hamartoma considered pathognomonic for Cowden disease. Classically, LD has a progressive and insidious onset of symptoms. In this case report, we present a patient having rapid neurological deterioration from acute-onset LD. There are only three reported cases of acute LD presentation. A 22-year-old female presented to the emergency department with diplopia, dysarthria, dysphagia, and gait instability which developed within 6 h. A non-contrast CT scan revealed diffuse attenuation in the left cerebellum and mild ventricular dilatation. LP revealed no organisms. Magnetic resonance imaging revealed salient "tiger stripe" appearance of the left cerebellar cortex and effacement of the fourth ventricle. The patient subsequently underwent suboccipital craniotomy and gross total resection of the lesion. The tumor histology showed distortion of normal cerebellar architecture with dysplastic ganglion cells, loss of Purkinje cells, atrophy of the white matter, and expansion of cerebellar folia. Findings were consistent with adult-onset Lhermitte-Duclos disease.