Abstract Background: Systemic Juvenile Idiopathic Arthritis (sJIA) is a rare systemic inflammatory disease wich represents a subtype of a Juvenile Idiopathic Arthritis (JIA) according to the Classification of Edmonton. It is distinguished from other subtypes by its pathophysiology, systemic extra-articular involvement and treatment. This disease has strong similarities with Adult-onset Still`s Disease (AOSD). These diseases differing mainly in the diagnostic criteria. Objective: To identify the similarities between sJIA and AOSD given the benefits that a change to the classification criteria would make. Methods: Research Portuguese and English scientific papers in Pubmed database and published between 1992 and 2019 using the keywords “juvenile idiopathic arthritis”; “systemic juvenile idiopathic arthritis”; “Still´s disease” and “Adult-onset Still`s disease”, having been selected the most clinically and historically relevant ones. Results: The pathophysiology of SJIA has marked differences when compared to other subtypes of JIA, with a more prominent role of innate immunity and an increased production of interleukins (IL-1, IL-6 and IL-18). The sJIA presents several pathophysiological, clinical and analytical similarities with AOSD. Regarding the current diagnostic criteria (Edmonton´s for sJIA and Yamaguchi´s for AOSD), they differ mainly in the presence of arthritis, which is an essential criterion in the classification of Edmonton, while according to the classification of Yamaguchi, it is only required the presence of arthralgia. The requirement of arthritis in the initial presentation leads to delayed diagnosis in patients who present with other features of sJIA. Concerning treatment, new drugs are currently used in sJIA, allowing for a more oriented therapy in those systemic symptoms are the main problem in the long term. Conclusions: In a pathology associated to great mortality and morbidity as is sJIA, a timely diagnosis is essential, so a highly suggestive clinical history of sJIA, even in the absence of arthritis, can not be disregarded. Thus, a review of the criteria will allow a faster detection of the pathology in question and an earlier onset of the therapy aiming at a better prognosis.