Juvenile dermatomyositis (JDM) is a multisystem inflammatory disease of unknown etiology that affects primarily the skin and muscles. Although the prognosis of JDM has improved considerably in the last three decades, a number of patients may develop irreversible damage due to the disease activity or its treatment. This damage may cause permanent disability and affect the quality of life of patients and their families. In the clinical management of patients with JDM, there is, therefore, the need of monitoring the level of disease activity, the accrual of organ damage, and the impact of the illness on patients' daily living. A reliable assessment of these different aspects of disease requires the availability of well-designed and standardized clinical tools. In the recent years, there has been increasing collaborative effort to devise new assessment measures and these measures have been included into disease activity and damage core sets of outcome variables that have been developed through international consensus. In addition, preliminary definitions of clinical improvement for patients with JDM and other idiopathic inflammatory myopathies have been created. In this review, the latest advances in the development of standardized instruments for the clinical assessment of JDM patients are illustrated and the recent international efforts that have led to the development of core sets of outcome measures and to preliminary definitions of improvement for JDM clinical trials are summarized.