Next tonight making babies in modern times. This week we told you about the explosion of young women recruited to donate their eggs to strangers. Tonight men and the consequence of something that... See More
Next tonight making babies in modern times. This week we told you about the explosion of young women recruited to donate their eggs to strangers. Tonight men and the consequence of something that started more than 50 years ago. There are now so many startled children learning they have the same father. Abc's ron claiborne investigates. You are the biological father of 533 children. What? Reporter: "Delivery man" is about a sperm donor who finds out he's fathered hundreds of children. Far fetched? Well, do you know any young people who look like this man? He's todd whitehurst, who as a young grad student earned $12,000 donating sperm two to three times a week for more than three years. You do the math. One day, years later, he was contacted by a 14-year-old girl who told him he was her father. My first reaction was just to be stunned. Reporter: Since then, he's met three of his other donor dozen all together. How do you know you don't have 50, 100 children, 150? I don't know but it's certainly possible. It's the wild west. There's essentially no sheriff in town. In this area which has become quite large, quite lucrative and is literally involved in the most intimate area of peoples' lives. Reporter: Some countries limit the number of children a sperm donor can have. In the united kingdom the limit is ten. Children can find their biological dad and his health history. In england and in most of europe it's illegal to have anonymous sperm donation. Reporter: In the u.S. More than 2 million children have been born from donated sperm. A website has been connecting them to their fathers and half siblings for the last 13 years. Reporter: Adrianna and kyle found each other through that registry. The donor doesn't have any legal or social binding, but half sister, that is cool. Reporter: So far, more than 10,000 connections have been made. Todd whitehurst eventually met his daughter, virginia. We have a remarkable amount in system. It's surprising really. It's like we're related or something. Reporter: One more version of the modern american family. Ron claiborne, abc news, new york.
This transcript has been automatically generated and may not be 100% accurate.