Introduction: Decision-making regarding admission to UK intensive care units is challenging. Demand for beds exceeds capacity, yet the need to provide emergency cover creates pressure to build redundancy into the system. Guidelines to aid clinical decision-making are outdated, resulting in an over-reliance on professional judgement. Although clinicians are highly skilled, there is variability in intensive care unit decision-making, especially at the inter-specialty level wherein cognitive biases contribute to disagreement. Method: This research is the first to explore intensive care unit referral and admission decision-making using the Critical Decision Method interviewing technique. We interviewed intensive care unit (n = 9) and non-intensive care unit (n = 6) consultants about a challenging referral they had dealt with in the past where there was disagreement about the patient’s suitability for intensive care unit. Results: We present: (i) a description of the referral pathway; (ii) challenges that appear to derail referrals (i.e. process issues, decision biases, inherent stressors, post-decision consequences) and (iii) potential solutions to improve this process. Discussion: This research provides a foundation upon which interventions to improve inter-specialty decision-making can be based.