PURPOSE: The Ocular Surface Disease Index (OSDI) is the most frequently used dry eye disease (DED) questionnaire, and the Symptom Assessment iN Dry Eye (SANDE) is the simplest and quickest to apply. We analyze the correlation and level of agreement between these two questionnaires in a large DED heterogeneous population to evaluate their performance and potential interchangeability. METHODS: Prospective, multicenter longitudinal survey-based study performed on patients diagnosed with DED by 99 ophthalmologists from 20/32 Mexican states. Questionnaires were applied in two consecutive visits to analyze the correlation between OSDI and SANDE to evaluate patients with DED clinically. Level of agreement was evaluated with Bland-Altman analysis, and internal consistency of instruments was evaluated individually and combined with Cronbach's alpha index. RESULTS: 3421 patients studied: 1996 (58.3%) women and 1425 (41.7%) men, aged 49.5 ± 15.4 years; 995 (29.1%) patients had aqueous-deficient, 1086 (31.7%) evaporative, and 1340 (39.2%) mixed DED subtypes. Normalized baseline scores were 53.7 (OSDI) and 54.1 (SANDE). After 36.3 ± 24.4 days between visits, scores were reduced to 25.2 (OSDI) and 21.8 (SANDE) points (p < .001). A positive correlation between questionnaires was found at baseline (R = 0.592; p < .001), follow-up (R = 0.543; p < .001) and change between visits (R = 0.630; p < .001). Using both questionnaires together improved the overall reliability of symptom evaluation at baseline (α = 0.7), follow-up (α = 0.7), and both (α = 0.7), compared to individual application (OSDI α = 0.5, SANDE α = 0.6)-the same improvements applied to all DED subtypes. Bland-Altman analysis revealed a differential bias of -0.41% at baseline and +3.6% at follow-up visits between OSDI and SANDE. CONCLUSIONS: We validated the correlation (high precision) between questionnaires in a large-scale population, demonstrating improved reliability (high accuracy) in evaluating DED when used together, challenging their interchangeable use. These results open a venue to improve recommendations toward a more precise and accurate diagnostic and therapeutic evaluation of DED by using OSDI and SANDE concurrently.