Patients undergoing the biological therapy require particularly intensive care. During numerous, systematically repeated monitoring visits, the patients’ documentation is enriched with a huge amount of data regarding their disease and treatment. Analysis of these data can help obtain a multi-dimensional evaluation of the effectiveness and safety profile of the therapy. This became an inspiration for the Polish scientific electronic register of children treated with biological therapies: “Long-term assessment of safety and efficacy of biological treatment in juvenile idiopathic arthritis” – the register of Polish patients. The registry started operating in April 2009. A year later it contained data of 218 patients suffering from juvenile idiopathic arthritis treated with biological agents: etanercept was used in 210 patients and adalimumab in 8 patients. The main aims of the registry are: 1) long-term assessment of the safety profile of the applied treatment by recording and analyzing the adverse events; 2) long-term assessment of the effectiveness profile of the given treatment on the basis of the activity of the disease and patient’s quality of life. The registry contains data coming from the patients’ medical history concerning the beginning and the course of JIA, previous treatment with the assessment of its effectiveness and tolerance, the activity of the disease, the occurrence of autoimmunization diseases in the family and the analysis of the quality of life before starting biological therapy. On the basis of the data collected during regular appointments, the doctor fills in an electronic questionnaire of 35 questions concerning the somatic development and present course of treatment. The activity of the disease profile is being evaluated (according to Gianinni), the improvement profile ACR Ped is being calculated. In addition, the effectiveness profile of the treatment is being assessed by the doctor, the patient and his or her parents. Also, absences from school and the number of hospitalizations are taken into account. The safety profile is being established by noting down the adverse events. This paper presents the main assumptions of the registry, its structure and trends in the analysis of the data and a list of study centres participating in the register (Table I and II).