Forest inventories are evolving towards multipurpose resource surveys, broadening their scope by including additional topics such as biodiversity issues. Surprisingly, few quantitative surveys have been devoted to old-growth forests, even if they constitute the most acknowledged forest biodiversity icons. In this framework, the use of probabilistic sampling may provide an effective as well as rigorous support for monitoring and assessing old-growth forests. To this purpose, the present paper proposes a two-phase sampling scheme. In the first phase, a coarse survey of few floristic and stand structural attributes is carried out by means of small plots systematically placed on the study area. Subsequently, in the second phase, a fine assessment of a large number of ecological attributes is performed on a subset of enlarged plots selected among the first-phase ones by means of simple random sampling without replacement. The proposed sampling scheme is implemented for monitoring and assessing the old forests of Cilento National Park (southern Italy). Results and comments are provided as an exemplicative case study. ; L'articolo è disponibile sul sito dell'editore www.tandf.co.uk/journals/