The application relates to taking a sample of liquid contained in a flexible closed container, for example, a bag for collecting urine or blood. The problem to be resolved relates to piercing the wall of the container with a non- cutting piece, whilst obtaining a precise and clean opening for accessing the liquid and preventing any unintended flow or spill of liquid. The problem is solved according to the present invention by a device for taking a sample of liquid contained in a flexible bag (13, 14), which is characterised in that the device comprises a first section (20) having a base surface (21) and a film perforating element (22) protruding from the base surface (21). The device according to the invention further comprises a second section (23) having a base surface (24) surrounding a cavity (25), which is adapted for receiving the film perforating element (22) of the first section (20). The first section (20) has an adhesive surface surrounding the film perforating element (22), and the second section (23) has an adhesive surface surrounding the cavity (25). Furthermore, one of the two sections (20, 23) comprises an opening (26) in the base surface, inside of the adhesive surface (21).La solicitud se refiere a tomar una muestra de un líquido contenido en un recipiente cerrado flexible, por ejemplo, una bolsa para recolectar orina o sangre. El problema a resolverse se refiere a perforar una pared del recipiente con una pieza sin corte, mientras se obtiene una abertura limpia y precisa para acceder al líquido y evitar cualquier flujo no intencional o derrame de líquido. El problema se resuelve de acuerdo con la presente invención por un dispositivo para tomar una muestra de líquido contenido en una bolsa flexible (13, 14), el cual se caracteriza porque el dispositivo comprende una primera sección (20) que tiene una superficie de base (21) y un elemento perforador de película (22) que sobresale de la superficie de base (21). El dispositivo de conformidad con la i
