Adolescents and young adults (AYAs) with immune thrombocytopenia (ITP) exhibit distinct clinical features and needs, defying categorization as either adults or children. Previous findings revealed a 50% risk of chronic disease at 12 months, yet the long-term course remains unclear. This study aimed to delineate the clinical and laboratory characteristics of AYAs with chronic primary ITP. Data from patients aged 12-25 years with chronic disease at 1 year were extracted from three registries (PARC-ITP, CEREVANCE, CARMEN), covering the period from 2004 to 2021. Sustained complete remission off treatment (SCROT) occurring beyond 12 months was defined as platelet count >100 × 109/L without treatment for at least 12 months, independently of the previous treatment strategy. A total of 427 AYAs (64% female) with chronic primary ITP were included. Clinical information was available for ~100% of patients at initial diagnosis, 6- and 12-month follow-ups, and for 88%, 77%, and 59% at 24, 36, and 48 months, respectively. Over time, clinical features improved gradually, with fewer patients requiring treatment. Throughout the follow-up period, second-line drug use increased steadily among treated patients, without impacting the need for corticosteroids and intravenous immunoglobulins. The proportion of new patients achieving SCROT at 24-, 36-, and 48-months FU was 10% (38/375), 9.5% (31/327), and 12% (30/250), respectively, including 23 who underwent splenectomy. AYAs achieving SCROT between 12-36 months displayed higher platelet counts in the first year (excluding the initial period) and received fewer intravenous immunoglobulin treatments beyond 12 months compared to those with ongoing disease.