A dilator assembly for percutaneous dilatational tracheostomy includes a dilator element having a wall and a proximal end part extending into a distal tip part via an intermediate part. The wall has a substantially U-shaped cross section defining a dilator opening. The assembly extends towards the distal tip part. The dilator assembly is part of a tracheostomy device. The device has a first branch for arranging inside the trachea, and a second branch co-operative with the first branch. The first branch has a first end and a receiving member while the opposing second end has a first coupling part. The second branch has a first end with a guide for a neck penetration member and an opposing second end with a second coupling part for coupling with the first coupling part of the first branch. The first and second branches are detachably coupled together at their respective second ends.