<i>Background/Aims:</i> Abnormal inflammatory response has been associated to the pathogenesis of Alzheimer’s disease (AD) and may be a marker of an ongoing neurodegenerative process. The aim of this study was to evaluate the serum levels of interleukin-1β (IL-1β) in patients with mild cognitive impairment (MCI) and AD. <i>Methods:</i> One hundred and sixty-three older adults (58 with mild to moderate AD, 74 with MCI and 31 healthy controls) were recruited for this study. Serum IL-1β levels were measured by ELISA. Patients with MCI were subcategorized in single-domain amnestic (aMCI), nonamnestic (naMCI), and multiple-domain (mdMCI) subtypes. <i>Results:</i> Patients with AD and MCI (all subtypes) had a significant increase in serum IL-1β levels as compared to controls (p = 0.03). Patients with mdMCI had serum IL-1β levels comparable to those with AD, and significantly higher than those observed in aMCI and naMCI (p = 0.02). <i>Discussion:</i> The present study provides evidence that inflammatory mechanisms, represented by elevated IL-1β, are observed in patients with MCI, specifically in those with impairment in multiple cognitive domains. As these patients are at higher risk of conversion to dementia, we propose that an increased serum IL-1β level is a stage marker of the ongoing brain neurodegeneration in the continuum between normal ageing and AD.