The Spinnaker Tower was last night lit up like a candle on a birthday cake for the first of a series of events to celebrate the landmark turning five years old.
The lights were changed by ITV weatherman Simon Parkin, who had the honour of pressing the red button mounted specially on the rail around the first viewing platform's glass floor.
He said: 'What an honour, to be part of the birthday celebrations of something that in such a short space of time has become such a landmark.'
In the tower's five-year history more than two million people have visited it, and it has generated around 70million for the local economy.
And it was even given international recognition during the Beijing Olympics, when a map of the world, tracking the passage of the Olympic torch, featured a small Spinnaker Tower in Portsmouth.
Speaking on the first viewing platform, 100m up in the air, the tower's operations manager Simon Wildgust said: 'I think it's important to recognise the impact the tower has had on the city.
'It's an asset for the city, and for the south coast as a whole.'
The celebrations continue on Monday, when a new cafe opens on the upper viewing deck.
And everyone with a PO postcode - not just those living in the city - will benefit from discounted entry to the attraction.
'We just want to celebrate,' added Mr Wildgust.
'The tower is just fantastic - and of course I'm not biased!'