Introduction - Tree architecture is a fundamental part of a functional structural plant model. This is particularly evident in perennial tree crops where the structure of the plant influences the position of source and sink organs, as well as light interception inside the canopy, and serves as storage pool for exceeding carbohydrates. Therefore, a precise description of tree 3D structure is essential to realistically allocate carbohydrates in a FSPM (Costes et al., 2006). Hazelnut tree architecture has different characteristics compared to other fruit tree crops that have been modelled (i.e., peach, mango, apple, and kiwi). It is a monoecious species. Female flowers are grouped into inflorescences located into mixed buds, while male flowers are arranged into inflorescences in the apical position of sylleptic shoots. Each node could bear more than one bud and, the following year, the new shoots are much shorter than the shoots from which they were born. The present study aimed to analyse hazelnut one-year-old shoots 'architecture in order to build the structural part of L-HAZELNUT: a functional structural plant model of hazelnut (Corylus avellana). Material and Methods - Own-rooted tree clones of C.avellana, cultivar “Tonda di Giffoni”, were chosen, during winter, in 2020 and 2021 in Deruta (Italy). Plants were normally irrigated and fertilized. No pruning occurred during the two years. 104 one-year-old proleptic shoots were sampled according to four length categories: short (Sh) when shorter than 5 cm, medium (Me) when they were between 5 and 20 cm, long (Lo) when they were between 20 and 40 cm, and very long (VLo) when longer than 40 cm. For each shoot, diameter, length, and number of nodes were recorded. From the base of the shoot to its tip, the fate of each node was noted. Four fates are distinguished in C.avellana: blind nodes, vegetative buds, sylleptic shoots and mixed buds. In the year subsequent to sampling, the same measurements were repeated on the latera