© 2022, Associacao Arquivos de Neuro-Psiquiatria. All rights reserved.Alzheimer’s disease (AD) is the most common cause of dementia in the elderly. Although AD treatment is still insufficient despite all the recent developments, detection and treatment in the early stage of disease have provided more clinical benefits. Objective: In this study, we aimed to use the critical flicker fusion (CFF) threshold test to diagnose AD in the early stage. Methods: In this study, 120 patients (above 65 years of age) and 50 control groups who were admitted to geriatrics outpatient clinic and diagnosed in early-and middle-stage AD were included. The remaining 58 patients and 25 healthy volunteers underwent comprehensive geriatric assessment and CFF testing. Results: The mean CFF value of AD group was significantly lower than the control group (36.44±7.00 vs. 44.24±3.82, p<0.001, respectively). There was a significant difference in standardized mini-mental state examination (MMSE) score in both groups (18.05±5.25 vs. 25.96±2.85, p<0.001, respectively).There was also a positive correlation between CFF value and MMSE score (p<0.001, r=0.459). Thirty-four patients were in the early-stage AD group and 24 patients were in the middle-stage AD group. There was a significant difference in CFF values between the three groups when we compared the patients in early-and middle-stage AD and control groups (p<0.001). The mean CFF values in patients with early-and middle-stage AD were 37.93±7.33 and 34.97±7.43, respectively. The mean age, gender, education level, and the number of drugs used did not show a statistically significant difference in both groups (p>0.05). The cutoff value for the CFF variable was determined as 39 Hz [p<0.001; area under the curve (AUC)=0.852; sensitivity=70.69% (95% confidence interval [95%CI] 57.3–81.9); specificity=92.00% (95%CI 74.00–99.00)]. Conclusions: There is a significant difference in mean CFF values between AD and healthy groups. CFF testing may play an important role in diagnosing AD in the early stage.