Autonomic instability is well recognized in Guillain-Barré syndrome (GBS), particularly in the acute inflammatory demyelinating polyneuropathy subtype. Hypertension occurs in up to two-thirds of children with GBS but is rarely the main presenting feature. We describe a teenager who presented with tachycardia, dizziness, flushing, and significant hypertension as well as ascending limb weakness and sensory disturbance with areflexia. Because the predominant initial concern was hypertension, she was referred to pediatric nephrology and appropriate investigations for hypertension were conducted. Her neurologic findings prompted a neurology referral, and a diagnosis of GBS was made. The investigations for hypertension subsequently revealed increased urinary normetadrenaline levels in a range consistent with pheochromocytoma, prompting the question of dual pathology. Both autonomic symptoms and urinary metadrenaline levels subsided with GBS resolution, and further investigations excluded the diagnosis of pheochromocytoma. Our case highlights that significant dysautonomia can occur in children with GBS, with hypertension being a prominent early feature. Recognition that urinary metadrenalines can increase to levels seen in pheochromocytoma is important in avoiding diagnostic confusion.