The yellow fever vaccine is generally considered safe and well tolerated, but it is associated with two serious adverse events that are unique to it: yellow fever vaccine-associated neurologic disease (YEL-AND) and yellow fever vaccine-associated viscerotropic disease (YEL-AVD). People at increased risk of these serious adverse events include those aged 60 years and over and people with a history of thymus dysfunction or thymectomy. Since 2019, thymectomy for any reason is a contraindication to yellow fever vaccination in the UK. The thymus gland may be removed during cardiac surgery (incidental thymectomy). Therefore, it is important to take a detailed cardiac surgery history as part of a pre-vaccination risk assessment. This article discusses recent changes to UK guidance on yellow fever vaccination to help healthcare professionals working in yellow fever vaccination centres to decide whether this vaccination is advisable.