A poll of 2,000 adults who have a brother or sister, found 51 percent have a competitive relationship with their siblings over things such as their career and being a homeowner.
Many still fight about who is the favourite child as they continue to try and outdo each other.
It also emerged that almost 20% admitted they had felt a rivalry with their siblings at every stage of their lives.
The study showed that adult siblings will argue twice a month on average.
But a quarter of siblings believe that the rivalry motivated them to do better things in life.
TOP 10 AREAS SIBLINGS ARE COMPETITIVE IN:
1. Career success
2. Housing success – who bought their house first, who has the biggest house
3. Who is the favourite ‘child’
4. Holiday destinations
5. Sport success
6. Cooking skills
7. Who drives the best car
8. Who got the best grades at school
9. Impressing our parents with gifts
10. Parenting skills