Boris Johnson met with volunteers from the Royal Hospital for Neuro-disability (RHN), to hear more about their work with patients.
Volunteers at the hospital work with people living with severe disabilities helping to greatly improve their quality of life.
The Mayor of London said: "Volunteers like the wonderful people I met today have a huge impact on the lives of Londoners and communities across the capital.
"It is this dedication and enthusiasm that is at the heart of our Team London programme and I urge other Londoners to think about volunteering, which is making a positive difference to life in our great city."
Carol Mackay, who has been volunteering at the RHN for over 10 years, said: "I was really impressed with how much interest the Mayor showed in the RHN and in the value of volunteering in general."
Angus Somerville, Chief Executive at the RHN said: "Our volunteers make such a huge difference to patients here at the RHN.
"Whether it’s gardening, assisting with adapted sports or simply sitting with people and reading the paper, their contribution is so valuable and it’s brilliant to see them recognised."
The Volunteering Service at the RHN is completely funded through donations made to the charity - just one of the many vital services provided at the hospital through charitable contributions.