The purpose of this study was to compare three commonly used scoring systems of acute mountain sickness (AMS)-the 5-item Lake Louise Self-report (LLS), the 11-item abridged version of the Environmental Symptoms Questionnaire (ESQ-III), and a 100 mm visual analog scale (VAS)-on climbers (N=63; 34.6±9.9 years) making a 1-day ascent of a 5640 m peak after a rest of ~10 h at 4260 m. The prevalence of AMS was 63% when defined as LLS ≥3, 49% when defined as either LLS ≥5 or ESQ-III ≥0.7, and 41% when defined as the combined LLS and ESQ-III criteria. Despite the agreement in prevalence between the LLS ≥5 and ESQ-III ≥0.7, there was a discrepancy in AMS classification in 16% of the cases. A VAS cut-off point corresponding to the combined LLS and ESQ-III criteria was 16 mm. The sensitivity and specificity of the VAS for diagnosing AMS compared to combined LLS and ESQ-III criteria were 85% and 92%, respectively. All of the scoring systems were significantly correlated (τ=0.60 to 0.73, p<0.01); however, residual scores were large. We cannot recommend interchanging the diagnostic results from the LLS, ESQ-III, and VAS, and standardization is needed for the administration of the VAS.