Since 1991, sperm donors in the UK have had the legal right to withdraw consent for the use of their sperm in fertility treatment. This has the potential to adversely affect patients. It may mean that previous recipients of a donor’s sperm cannot have further children who are full biological siblings to an existing child, and that embryos created from the donor’s sperm and a patient’s eggs must be destroyed. We have informally investigated withdrawal of consent by sperm donors donating after 1 April 2005, when lifelong anonymity for gamete donors ended.