The interim emergency department at Letterkenny General Hospital has opened to walk-in patients.
The building was extensively damaged by flooding three weeks ago, which led to all local emergency cases being diverted to hospitals in Derry, Sligo and Enniskillen.
The hospital said any non-emergency patients should continue to contact their GP and should not attend Altnagelvin Hospital.
The interim emergency department opened to ambulance admissions at the weekend.
Hospital manager Sean Murphy said the phased re-opening of the department has been a success and the hospital is continuing to extend the areas "for which we can accept ambulance and GP referrals over the next 24 hours".