The primary aim of the study was to evaluate the incidence of de novo major involvement during follow-up in a cohort of patients with Behçet's syndrome (BS); the secondary aim was to analyse the epidemiological profile and the long-term outcome of those patients who developed new major involvement. Among our cohort of 120 BS patients, we evaluated all subjects who had no major organ involvement during the early years of their disease; specifically, at disease onset, the 52% of the cohort presented a prevalent mucocutaneous involvement. The primary outcomes were represented by the following: Hatemi et al. (Rheum Dis Clin North Am 39(2):245-61, 2013) the incidence of de novo major involvement during the follow-up and Hatemi et al. (Clin Exp Rheumatol 32(4 Suppl 84):S112-22, 2014) the use of immunosuppressive drugs during the follow-up. We have defined the development of de novo major involvement during the follow-up as the occurrence of severe ocular, vascular or CNS involvement after a latency period from the diagnosis of at least 3 years. Among 62 patients characterized by a mild onset of disease, we observed that after at least 3 years from the diagnosis, 21 BS patients (34%) still developed serious morbidities. Specifically, three patients developed ocular involvement, nine patients developed neurological involvement and nine patients presented vascular involvement. Comparing main epidemiological and clinical findings of the two groups, we observed that patients who developed de novo major involvement were more frequently males and younger; furthermore, 95% of these patients were characterized by a young onset of disease (p < 0.001). Being free of major organ complication in the first years of BS is not necessary a sign of a favourable outcome. Globally, the development of de novo major involvement during the coursfce of BS suggests that a tight control is strongly recommended during the course of the disease.