Abstract Background Patients presenting with infection to the ambulance are common, but risk factors for poor outcome are not known. The primary aim of the current study was to study the association between variables measured in the ambulance and mortality among adult patients with and without infection. The secondary aim was to study the association between these variables and mortality in a subgroup of patients who developed sepsis within 36 h. Methods Prospective cohort study of 553 ambulance patients with, and 318 patients without infection, performed in Stockholm during 2017–2018. The association between 21 variables (8 keywords related to medical history, 6 vital signs, 4 blood tests, and age, gender, comorbidity) and in-hospital mortality was analysed using logistic regression. Results Among patients with infection, inability of the patient to answer questions relating to certain symptoms such as pain and gastrointestinal symptoms was significantly associated with mortality in univariable analysis, in addition to oxygen saturation 110 /min, Glasgow Coma Scale (GCS)