The paper presents a comparative study of a well-established steelwork design standard, the American AISC LRFD, and the new European code for the design of steel structures, Eurocode 3. First, the paper compares the formulation of both codes in order to identify similarities and differences. Then the comparative study is performed for a rolled I-section with different slenderness. Most frequent cases of linear and parabolic moment distributions are considered. The results are presented graphically by means of interaction diagrams to facilitate their interpretation and to detect differences in resistance. The comparative study shows that the resistance capacities given by LRFD and the two methods of EC3 can differ appreciably when slenderness is high and the member is subjected to linear moment distribution with opposite end-moments. Finally the paper presents a LRFD-EC3 combined approach which can be used to estimate the resistance of beam-columns.