<p>Chronic alcohol exposure may trigger astrogliosis—a process involving hypertrophy and upregulation of astrocyte-specific markers following neuronal stress or injury—as suggested by trends in preclinical studies. However, in vivo evidence of astrogliosis in alcohol use disorder (AUD) is lacking. Here, we investigated the status of the astrocyte marker MAO-B -an enzyme predominantly expressed in astrocytes and upregulated during astrogliosis - using [¹¹C]SL25.1188 positron emission tomography imaging in healthy controls (n = 28) and people with AUD after 3.5 ± 3.7 (n = 24) and 24 ± 7 days (in a subset: n = 8) of abstinence. Clinical symptoms of AUD were assessed, alongside peripheral markers of astrocyte activation and neuronal injury: glial fibrillary acidic protein (GFAP) and neurofilament light chain (NF-L), respectively. While mean [¹¹C]SL25.1188 binding did not differ significantly between people with and without AUD at either abstinence time-point, binding was notably more variable in AUD and inversely correlated with AUD severity, withdrawal and anxiety (p &lt; 0.05). Plasma GFAP and NF-L were elevated in people with AUD. Daily cigarette use was associated with lower [¹¹C]SL25.1188 binding in people with AUD (−40%) and control participants (−33%). These findings reflect variability in MAO-B binding in AUD and support a potential link between lower MAO-B and greater clinical severity. The observed association between cigarette use and lower MAO-B binding replicates prior reports and extends this observation to AUD. The relationship between higher MAO-B binding and lower AUD severity may reflect compensatory reactive astrogliosis. Understanding whether MAO-B status reflects a beneficial or detrimental astrocytic response in AUD may be important for glial-targeted treatments.</p>