Patients with head and neck cancer (HNC) often experience cognitive impairment. However, the relationship between cancer and Alzheimer's disease (AD) remains unclear. We aimed to elucidate the relationship between patients with HNC and their subsequent AD development. This retrospective study used data from a nationwide representative cohort sample, the Korean National Health Insurance Service Cohort. The cancer group was defined based on the presence of diagnostic codes for HNC (C00-C14 and C30-C32). After matching the independent variables with a propensity score of 4:1, a total of 2304 people without HNC and 576 with HNC were enrolled in this study. Hazard ratios (HRs) of AD incidence (per 1000 person-years) and 95% confidence intervals (CIs) in HNC patients were calculated. The incidence of AD was 14.92 in HNC patients and 9.77 in non-cancer patients. Additionally, the HNC group was found to have a higher risk of developing AD compared with the non-cancer group. Female and middle-aged HNC patients had a higher risk of developing AD events compared with other subgroups. Surprisingly, during the observation period, the risk of developing AD was relatively high within the first year after HNC diagnosis. In conclusion, our study suggests that HNC and AD are positively correlated.