Assessments of history and body temperature are cornerstones of the diagnostic workup in all patients presenting to emergency departments (ED). Yet, the objective measurement of temperature and the subjective perception of fever can differ. This is a secondary exploratory analysis of a consecutive all-comer study, performed at an adult ED in Switzerland. Trained medical students interviewed all patients if fever was present. Altered temperature (>38.0 °C/<36.0 °C) measured at triage using an ear thermometer was used as the reference standard for diagnostic performance. In case of a disagreement between fever symptoms and altered temperature, discordance was noted. Outcome measures for case severity (acute morbidity, hospitalization, intensive care, and in-hospital mortality) were extracted from the electronic health records. Odds ratios (OR) for discordance between signs and symptoms and outcomes were calculated. Among 2183 patients, 325 patients reported fever symptoms. The sensitivity of fever symptoms as a test for altered temperature was 36.3%. Specificity was 91.5%. The negative predictive value was 84.1%, positive likelihood ratio was 4.2 and negative likelihood ratio was 0.7. The adjusted OR for discordance between fever symptoms and altered temperature was 1.71 (95% CI: 1.2–2.44) for acute morbidity, 1.56 (95% CI: 1.13–2.15) for hospitalization, and 1.12 (95% CI: 0.64–1.59) for intensive care. Unadjusted OR for mortality was 1.5 (95% CI: 0.69–3.25). Fever symptoms and altered temperature broadly overlap, but presentations can be stratified according to concordance between signs and symptoms. In case of discordance, the odds for acute morbidity and hospitalization are increased. Discordance may therefore be further investigated as a red flag for a serious outcome.