Reasons for size dependence of rotation capacity of plastic hinges are discussed. The increase of ductility with decreasing member size is interpreted from the viewpoint of fracture mechanics of concrete. The results of the introductory test series on simply supported slender beams loaded in three-point bending are discussed. A new model for the calculation of the rotation capacity is described, which takes into consideration the strain localisation in the damage zones in the hinge region. In particular, the way of implementing the Fictitious Crack Model, the Compressive Damage Zone Model and a new fracture mechanics based bond model that takes into account the steel stress level (e.g. the yielding of reinforcement) is explained. The results of parameter studies on size effects in plastic hinges are described. Special attention is given to the influence of reinforcement arrangement and of the flexural crack pattern. In conclusions the importance of the size effect in practical design situations is examined and the need for altering the existing design rules in the light of the possible member size dependence of the rotation capacity of plastic hinges is evaluated