Background <p>There is much debate on how scarce medical resources such as transplant organs should be allocated: in the UK, the NHS uses the principles of sickest first, prognosis and waiting list time – but not age [1]. Furthermore, it has recently been reported that in the UK younger patients tend to wait much longer than older patients for a liver transplant. The current study investigates younger and older lay people’s preferences for the allocation of liver transplants using four criteria,the patient’s age, time spent on the waiting list, pre-transplant life expectancy and post-transplant life expectancy.</p> Methods <p>In an online study, lay participants (<i>N</i> = 400) rated 16 hypothetical patients in terms of priority to receive an available donor liver, using only information on patients’ age, time spent on the waiting list, pre-transplant life expectancy and post-transplant life expectancy. The relative ‘importance’ of the criteria in making decisions was indexed using a standardised effect size measure (generalised eta-squared).</p> Results <p>Pre-transplant life expectancy (‘sickest first’) was associated with the largest effect size, followed by post-transplant life expectancy (‘prognosis’), then age (‘youngest first’) and finally waiting list (‘first-come, first served’). In addition, participants assigned higher priority ratings to young patients, patients who had been on the waiting list for a long time, patients with a low pre-transplant life expectancy, and patients with a high post-transplant life expectancy. Both age groups prioritised younger over older patients, but younger participants prioritised younger over older patients to a greater extent than did older participants. There was no evidence for in-group bias. Additionally, younger participants showed a stronger prioritisation of patients with a long waiting time and patients with a low pre-transplant life expectancy compared to older participants.</p> Conclusions <p>Lay individuals were able to effectively use the four allocation principles in a practical scenario to assign priority ratings to potential liver transplant recipients. The findings are consistent with previous findings that lay individuals see ‘sickest first’ (pre-transplant life expectancy in this case) as being the most important criterion for the allocation of a scarce medical resource. However, the findings also reveal that both younger and older individuals support the notion that ‘youngest first’ is also an important criterion, something not currently reflected in the NHS allocation policy.</p>