A poster urging outpatients to inform hospitals if they have to cancel
The cost of missed hospital appointments in one month at one NHS trust is enough to employ nine nurses for a year, according to health chiefs.
North West Wales NHS Trust, which runs Ysbyty Gwynedd in Bangor, said 1,863 outpatient appointments were missed in November last year, costing £279,450.
It has urged people to be in contact if they cannot attend an appointment.
There are 300,000 missed appointments in Wales a year, and calls have been made for such patients to be charged.
Last month, Cardiff and Vale NHS Trust said missed appointments cost it an estimated £3m per year.
North West Wales NHS Trust said up to £1.5m a year was potentially being wasted by people who failed to turn up to outpatient appointments.
The trust is to include an information flyer with each outpatient appointment letter, reminding patients to say if they cannot attend.
Denise Williams, the trust's service improvement manager, said: "Unfortunately, approximately 1,600 patients fail to turn up for appointments every month.
"To put this into context, the money associated with the appointments missed in November 2008 equates to employing nine registered nurses for a year, or 43 total hip replacement operations a month.
"We are therefore appealing to those who are unable to attend appointments to notify the trust as soon as possible, calling the number on their appointment letter.
"This will allow us to offer that appointment to someone else, which will also bring down the waiting lists."
She said a service where patients attending an outpatient appointment receive a telephone call a few days before to remind them had also been introduced.
Last month, the Welsh NHS Confederation said hospitals should consider charging patients who fail to arrive for their appointments without notification.
The proposal came as Cardiff and Vale NHS Trust released figures which showed more than 200 outpatients appointments went unattended every day.
Across Wales, 300,000 patients fail to attend appointments every year.