The chairman of NHS Greater Glasgow and Clyde, Andrew Robertson, cut the first sod of the new Vale of Leven Centre for Health and Care to mark the beginning of construction.
The health centre, which is being built on the Vale of Leven hospital site, is based on a design which will support the needs of the local community.
Mr Robertson said: "I am delighted to be cutting the first sod in this significant development which when completed in 2013 will offer a state-of-the-art health and care facility for the local population.
"In its Vision for the Vale, the Health Board made an explicit commitment to delivering a substantially enhanced replacement for the existing Alexandria Medical Centre on the Vale of Leven Hospital site.
"In beginning the construction of this facility we will have delivered the Vision for the Vale in full."
The facility will provide three large general practices, dietetics, podiatry, speech and language therapy, primary care mental health, physiotherapy and dental care.
It will also be the base for the local district nursing team, prescribing support team, integrated health and social care team and will offer training and education facilities.
Health Secretary Nicola Sturgeon said: "I am delighted work is now under way on the new Alexandria Centre on the Vale of Leven hospital site.
"The £20.8m health and care centre will enable improved access for local communities to a variety of services."
Keith Redpath, director of West Dunbartonshire Community Health and Care Partnership, said the delivery of a new health and care centre has been an ambition within West Dunbartonshire for more than a decade.
He added: "Our vision is that the new centre will create a welcoming and therapeutic environment for the people from the local area to use."