We construct the creation operator of a vortex using the methods developed for monopoles. The vacuum expectation value of this operator is interpreted as a disorder parameter describing vortex condensation and is studied numerically on a lattice in SU(2) gauge theory. The result is that vortices behave in the vacuum in a similar way to monopoles. The disorder parameter is different from zero in the confined phase, and vanishes at the deconfining phase transition. We discuss this behaviour in terms of symmetry. Correlation functions of the vortex creation operator at zero temperature are also investigated. A comparison is made with related results by other groups.