Purpose - This paper's aim is to focus on the design, manufacture and test of a stiffened panel in composite material with integrated longitudinal foam-filled stiffeners, spar and rib caps, using one-shot liquid infusion (LI) process, reducing weight and number of subparts respect to metallic reference baseline P180 Avanti vertical fin. Design/methodology/approach - Extensive activities in computational applications in order to improve the efficiency of the design process finite element analysis/structural sizing codes have led to an optimised engineering design process that resulted in a successful stiffened carbon fibre reinforced polymer panel design in terms of weight and number of parts with respect to the metallic baseline. Findings - The composite panel has fulfilled all the design requirements (reduction of mass and number of parts with respect to the metallic reference baseline) overcoming the certification static test, and confirming the reliability of the theoretical analyses. Research limitations/implications - The composite aircraft components, conceived as unitized structure by one-shot process, guarantee not only a mass reduction, compared to aluminium components, but assure also the reduction of the number of subparts and of the assembly process cycle time. On the other hand, the LI technology implies the development of more specific and advanced techniques to control the manufacturing and the weight. Practical implications - The stiffened panel is the most used component in the aircraft structures; the solution shown in this work can find applications in many parts of an aircraft. Originality/value - The results obtained in this work can be useful to those who work in aeronautical structural departments with the aim to reduce weight and subparts of the airframe.