Patients are being treated in two mobile operating theatres on a north Wales hospital car park while work is under way to upgrade existing facilities.
The first patients used the portable facilities at Ysbyty Glan Clwyd, Bodelwyddan, Denbighshire, on Monday.
They are being used while asbestos is removed from existing theatres.
The theatres are also being "refurbished to modern standards" as part of a £100m hospital development.
Neil Bradshaw, executive director of planning at Betsi Cadwaladr University Health Board, described the mobile theatres as a "state of the art facility".
He said they will help hospital staff "maintain services" whilst the "essential work" is carried out.
The theatres - occupying a consultants' car park at the side of the main hospital building - have an anaesthetics room and a recovery area and will be in use until spring 2012.
They have electrical and mechanical services, a ventilation system to provide clean air, a medical gas system and operating table.
The asbestos removal and theatre upgrade - costing £5.7m - is the first phase of the hospital development.
Other work includes improvements to facilities and services in accident and emergency and critical care.