Aims The aim of the present study was to evaluate whether there was an inflammation‐mediated link between Alzheimer's disease (AD) and type 2 diabetes mellitus (DM) status. Methods An age‐matched control group and patient groups designated as AD without treatment (AD); AD under cholinesterase inhibitors (AD‐CEI); DM without treatment (DM); DM under oral antidiabetic agents (DM‐OAD); AD under treatment, who had newly diagnosed DM (AD‐CEI+DM); and DM under treatment, who had newly diagnosed probable AD (DM‐OAD+AD) were studied. Serum inflammation status was evaluated by the determination of serum C‐reactive protein (CRP), tumor necrosis factor‐alpha, interleukin (IL)‐1β and IL‐6 levels. CRP levels were determined by an immunonephelometric method. The others were assayed by enzyme‐linked immunosorbent assay methods. Results IL‐1β levels were found to be significantly lower in the DM group than in the control group (P < 0.01). The AD group had significantly higher serum IL‐1β levels than the DM group (P < 0.01). IL‐6 levels were significantly higher in the AD and DM groups than in controls (P < 0.01 and P < 0.01). Serum tumor necrosis factor‐alpha and CRP levels in the AD (P < 0.05 and P < 0.001, respectively) and DM groups (P < 0.05 and P < 0.001, respectively) were significantly higher when compared with the controls. The presence of AD or DM or therapies of the diseases did not significantly change in serum tumor necrosis factor‐alpha levels. The AD‐CEI + DM and DM‐OAD+AD groups had significantly higher CRP levels than the AD‐CEI group (P < 0.05) and DM‐OAD groups (P < 0.001), respectively. Serum CRP levels showed a positive correlation with Mini‐Mental State Examination scores (r = 0.339, P < 0.01). Conclusion Our findings support the presence of a low‐grade systemic inflammation link between AD and DM. Geriatr Gerontol Int 2016; 16: 1161–1166.