Intermediate-care or high-dependency units can provide a level of care that lies between the intensive care unit (ICU) and general ward, but the patients who are most likely to benefit from such level of care remains uncertain. This nested case-control study assessed the incidence and risk factors of high-dependency patients requiring ICU admission and whether these admissions were associated with a worse outcome when compared to other emergency ICU admissions. Seventy-seven consecutive high-dependency patients requiring ICU admission (cases) were compared with 77 patients who did not require ICU admission (controls) and also 928 emergency ICU admissions from other areas. The incidence of high-dependency patients requiring ICU admission was 6.7% (95% confidence interval 5.3 to 8.2). High-dependency admissions from the ward (odds ratio 4.46, 95% confidence interval 1.55 to 12.78) or emergency department (odds ratio 4.48, 95% confidence interval 1.54 to 13.0) and a need for concurrent non-invasive ventilation, inotrope infusion and acute kidney injury (odds ratio 14.90, 95% confidence interval 3.79 to 58.3) was associated with a higher risk of ICU admission. Hospital mortality of the high-dependency patients requiring ICU admission was not significantly different from other emergency ICU admissions (odds ratio 1.08, 95% confidence interval 0.55 to 2.11). In summary, high-dependency patients requiring ICU admission were uncommon unless they had multi-organ failure and their hospital mortality was not significantly different from other emergency ICU admissions.