A method is presented that combines the modelling of cracks by distributed dislocation dipoles with developing plasticity represented by discrete dislocations moving along slip bands. Crack growth is due to the emission of dislocations from the crack tip along preferred slip planes. Eventual annihilation of dislocations occurs by reunion with the corresponding displacement steps of the crack surface. Crack surface overlap is not allowed. The equilibrium state for each load increment is solved iteratively, allowing various crack geometries. The method is applied to the problem of a short edge crack growing in mode I due to fatigue loading. It is shown that the development of a local plastic zone and the propagation of the crack can be monitored in detail.