their identity than married, heterosexual men. Potential donors with children are less inclined to want to meet offspring than potential donors without children (9 versus 30% in the review). Potential donors in a relationship are less inclined to consider contact with offspring than single potential donors (7 versus 28% in the review). From US data, 20% would actively want to know and meet offspring and 40% would not object if the child wished to meet but would not solicit a meeting themselves. From Swedish data, where only non-anonymous donation is permitted in clinics, 87% of potential donors had a positive attitude towards future contact with offspring, although 80% of these potential donors did not feel that the donor had any moral responsibilities for the child later in life. Also from UK data, 80% of potential donors did not feel responsible for whatever happened with their sperm after the donation. With variation between different studies, between 33% and 94% of potential donors want to know at least whether or not the donation resulted in offspring. Some of these potential donors merely wanted to know if a pregnancy had been achieved but did not want to know any specific information about the offspring (e.g. sex, date of birth). Other potential donors felt that knowing the outcome of the donation made the experience more meaningful. In comparison, a German study came to the result that 11% of donors actually asked about the outcome in the clinic where they donated. An Australian study concluded that potential donors who would still be willing to donate without a guarantee of anonymity were not automatically more open to extended or intimate contact with offspring. Donor tracking Even when donors choose to be anonymous, offspring may still find ways to learn more about their biological origins. Registries and DNA databases have been developed for this purpose. Registries that help donor-conceived offspring identify half-siblings from other mothers also help avoid accidental incest in adulthood. Tracking by registries Offspring of anonymous donors may often have the ability to obtain their biological father's donor number from the fertility clinic or sperm bank used for their birth. They may then share their number on a registry. By finding shared donor numbers, offspring may find their genetic half-siblings. The donor may also find his number on a registry and choose to make contact with his offspring or otherwise reveal his identity. Tracking by