A capsule for extracting a beverage from a substance in powder form, preferably ground coffee, by means of pressurized water, comprising a box-like body which contains the substance in powder form and has a base provided with an output port for the outflow of the extracted beverage, the output port being closed by an elastic crema forming septum which can open under the pressure of the water, the capsule further comprising a safety lid which is mounted on the box-like body at the base so as to increase the axial size of the box-like body, the lid comprising a shoulder which is engaged on the septum and is adapted to retain the septum within the capsule.