It's the type of toy that can keep youngsters happy for ours.
But now Lego is playing an extra special role in helping children at a hospital in Merseyside.
For the bricks have been used to build a model of a radiography machine to help explain to young cancer patients how radiotherapy works.
Radiographer Sarah Stead, at The Clatterbridge Cancer Centre, Wirral, originally built a basic model herself.
Then 10 year old Reece Holt, from Morecambe, who was treated with radiotherapy for a brain tumour, decided to make his own model of the machine.
He donated it to the centre to help other young patients.
It was such a success the centre then asked Legoland Discovery Centre, Manchester, if they could help build an even bigger version and staff were delighted when they agreed.
Reece has now accepted the new model on behalf of the hospital.