High strength steels are characterized by their high yield strength, but to guarantee a safe design, a sufficiently large fracture toughness value is also required. In this paper, the fracture toughness of three high strength steels (sigma(y) = 460-890 MPa) and their welds has been studied at low temperatures. Experimental results have been used to validate a statistical "weakest link" fracture model. The model takes into account the possibility of fracture nucleation in different types of particles and brittle phases, as well as the crack-arrest factors at the different microstructural barriers (particle-matrix interface and grain boundaries).