Thousands of hospital appointments are being missed every year, potentially costing the NHS millions of pounds.

Missed appointments, also known as did not attends (DNAs), can have an impact on waiting lists as well as the financial cost of wasting staff time.

Hospitals estimate someone not turning up can potentially cost about £100 for each appointment.

More than 121,000 patients did not show up for an outpatient appointment at hospitals across Sussex, working out at a possible cost of more than £12 million.

Some hospital trusts sometimes over-book outpatient appointments to minimise the effect of DNAs and staff can also get on with other jobs if they are left with unexpected free time.

Patients are urged to let hospitals know if they realise they are not going to be able to make their appointment because the slot could be given to someone else.

Some DNAs are unavoidable, such as patients moving away, having to deal with an unexpected emergency or not getting a letter or message beforehand giving them the time and date.

However others do not come along because they forgot about their appointment or felt they no longer needed one.

Figures from NHS England show Brighton and Sussex University Hospitals NHS Trust had 49,322 missed appointments between April 2012 and the end of March last year while there were 37,660 no shows at East Sussex Healthcare NHS Trust.

Western Sussex Hospitals NHS Trust reported 34,906 DNAs over the same period.

Brighton and Sussex University Hospitals, which runs the Royal Sussex County Hospital in Brighton and Princess Royal Hospital in Haywards Heath, has had problems with its centralised booking system, which may have contributed to some of the missed appointments.

A trust spokesman said: “When patients do not attend their appointments, it can have a negative effect on the efficiency of our outpatients department and cause delays for other patients to be treated.

“We have a number of initiatives in place to try to reduce the number of patients who do not attend their appointments, including a text service which reminds patients on their mobile phone of their appointment, and patients can also request to cancel or change their appointment online.”

Western Sussex Hospitals director of performance, Adam Creeggan, said: “Our outpatients are able to select the most convenient times for them and we have invested in technology that automatically sends a reminder to patients by text.

“We are also offering more outpatient services during evenings and on weekends to suit patients with work and family commitments.”