BACKGROUND: Migraine with unilateral cranial autonomic symptoms (UAS) is a putative migraine endophenotype with convincing response to trigeminal-targeted treatments that still needs a thorough characterization. OBJECTIVE: The objective of this article is to carefully investigate the clinical phenotype of migraine with UAS in a large group of patients for more accurate migraine diagnoses, improved clinical management, and better outcome prediction. METHODS: We studied 757 consecutive episodic and chronic migraineurs in a tertiary headache clinic with face-to-face interviews, detailing in depth their lifestyle, sociodemographic and headache characteristics. RESULTS: Migraineurs with UAS (37.4%) differed from the general migraine population with respect to longer attack duration (OR = 2.47, p < 0.02, having >72-hour long attacks), more strictly unilateral (OR = 3.18, p < 0.001) and severe headache (OR = 1.72, p = 0.011), more frequent allodynia (OR = 3.03, p < 0.001) and photophobia (OR = 1.87, p = 0.019). CONCLUSIONS: Migraine patients with UAS are characterized not only by symptoms due to intense peripheral trigeminal activation but also to central sensitization. Our study broadens the knowledge on the clinical and phenotypic characteristics of migraine with UAS, suggests pathophysiological implications, and supports the need for future prospective clinical studies.