BACKGROUND: Extreme heat is a public health priority in Australia with the health effects of cold poorly studied. A record-breaking cold winter prompted an institutional investigation into the epidemiology and outcomes of hypothermic presentations. METHOD: This was a retrospective cohort observational study of hypothermic emergency presentations between 7 July 2009 and 1 September 2016 with a temperature of /=65 years (p=0.002) and multimorbidity (Charlson comorbidity index >/=4, p=0.013) overrepresented in this subgroup. Among the non-exposure cohort, 55% were pensioners and 42% lived alone. Inpatient mortality was 11% overall and significantly higher in non-exposure vs. exposure cohorts (16% vs. 2%, p=0.01). Independent predictors of inpatient mortality included heart failure (p=0.04), metastatic malignancy (p<0.01), chronic kidney disease (p<0.05) and sepsis (p<0.01). In contrast, exposure related presentations were characterised by younger patients with intoxication due to alcohol and/or illicit drugs and psychiatric co-morbidity. CONCLUSION: Hypothermia is a marker of clinical and socioeconomic vulnerability. The dominant presentation of the elderly patient with multi-morbidity, and few social supports being found indoors, raises broader questions around the social determinants of health.