Missed appointments cost Epsom and St Helier hospitals £4.5m in 2011/12.
A total of 37,075 people failed to turn up to their appointments at St Helier, Epsom and Sutton hospitals.
Dr Ruth Charlton, joint medical director and consultant paediatrician, said: "We understand that people often have genuine reasons for missing an appointment, but it does have a real impact on the work that we do and our other patients.
"Missing an appointment with us can also have a knock-on effect on your own health too - we set our appointments to make sure you are well, and so it’s important that you try to come, even if you feel better.
"I would therefore like to ask that local people take note of their appointment, keep it in your diary and let us know if you can’t make it."
Across the UK 5.5m patients miss their appointments each year costing the NHS £700m.
Patients can manage, cancel or amend their appointments by visiting epsom-sthelier.nhs.uk/appointments or by calling 020 8296 2000