Abstract INTRODUCTION One of the pathological hallmarks of Alzheimer's disease (AD) is the accumulation of amyloid beta 42 (Aβ42). Decreased venous drainage may enhance Aβ42 accumulation. We aimed to compare venous cross‐sectional area (CSA) of AD patients to cognitively healthy controls. METHODS All patients underwent neurocognitive evaluation and brain magnetic resonance imaging, including time‐of‐flight sequence. Venous CSA was measured at the jugular foramen level. RESULTS Thirty‐nine AD/mild cognitive impairment patients and 20 cognitively healthy controls were included. Total venous CSA was smaller in the cognitively impaired group (mean CSA 139.77 mm 2 [SD: 32.22] vs 166.55 mm 2 [SD: 33.1], p = 0.004]. When divided, both internal jugular and non‐jugular systems were smaller within cognitively impaired patients; statistical significance was achieved only for the non‐jugular system (mean CSA 41.21 mm 2 [SD: 21.52] vs 54.5 mm 2 [SD: 27.31], p = 0.045). DISCUSSION There is an association between smaller venous systems and cognitive impairment, most prominently in the non‐jugular system. Venous narrowing may cause impaired venous drainage, leading to an accumulation of Aβ42. Highlights The non‐jugular venous system, including the vertebral plexus and pterygopalatine plexus, plays an important role in cerebral drainage. The total venous CSA is significantly smaller in cognitively impaired patients compared to healthy controls. Reduced venous drainage may contribute to the accumulation of Aβ and other waste products and potentially plays a role in AD pathology.