OBJECTIVES: This is the first study that assesses the economic costs of Type 1 Diabetes Mellitus (T1DM) in pediatric patients in Spain. The main objective of this study was to estimate direct healthcare costs (DHC) and direct non-healthcare costs (DNHC) of T1DM in children and adolescents. METHODS: CHRYSTAL (Costs and Health Related qualitY of life Study for Type 1 diAbetes meLlitus pediatric patients in Spain) is an observational study conducted in 2014 on a representative sample of 275 patients aged 1-17 years diagnosed with T1DM, distributed across 12 hospitals in Spain. The study followed a bottom-up-approach to costing from a societal perspective. Data on demographic and clinical characteristics, health resource utilization, and informal care were collected cross-sectionally from medical records and questionnaires completed by clinicians and patients´ caregivers. The reference year for unit prices was 2014. RESULTS: The average annual cost for a T1DM patient was €27,349. DHC amounted to €4,144, with statistically significant differences depending on glycemic control (HbA1c <7.5% versus HbA1c ≥ 7.5%): €3,683 versus €4,788 (p<0.05) and the existence of patient with acute and chronic complications (except hypoglycemia) and related comorbidities (with versus without): €5,777 versus €3,713 (p<0.05) after controlling for age and gender. The largest DHC were diabetes supplies (€2,035), outpatient visits (€841), and medication (€670). Average DNHC were €23,204. Informal care (the time that caregivers spend in T1DM related caregiving tasks) represented 97.5% of DNHC (€22,618) and 82.7% of total costs. CONCLUSIONS: T1DM in children and adolescent patients carries a considerable social economic burden, especially in terms of informal care, which accounts for the largest proportion of total costs associated to the disease. The results shed light on the allocation of T1DM related resources, and might enlighten T1DM policy priority setting in Spain.