A baby with Down's syndrome is born with more of chromosome 21 in some or all of their cells. It's also known as Trisomy 21.
People with the condition may lead active, healthy and independent lives into their 60s, 70s and beyond.
Most will have mild to moderate learning disabilities and some may have more complex needs.
It cannot be known before birth if a person will need any additional help and support.
Some health issues are more common in people with Down's syndrome but some are less common.