Alistair, 14, from Amersham, Buckinghamshire, became one of the first children to use the facilities in the Variety Club Building, which will be opened by the Princess of Wales. He is a long-term patient who suffers from Pfeiffer's syndrome, a rare neurological condition, and is now recovering after an operation to insert a probe to measure the pressure inside his head.
Today's ceremony will mark the culmination of the most successful fund- raising appeal of its type ever held in Britain. The campaign brought in pounds 54m in 20 months and closed six months ahead of schedule.
Although the money came from many different sources, the wing has been named the Variety Club Building in recognition of the efforts of the show business charity which raised pounds 3m.
The Government contributed another pounds 30m to build the wing which houses six operating theatres, a pathology laboratory, 119 beds including a paediatric intensive care unit, improved accommodation for patients' parents and other facilities.
Sarah Hopkins, spokeswoman for the hospital, said: 'The aim is to make the building as child-friendly and warm and welcoming as possible.' The Princess of Wales, the hospital's president, will make a rare departure from her decision to withdraw from royal duties to open the building. It was thought she would not attend the ceremony, but she decided to honour her only formally announced engagement of 1994.