Background: Multisystem inflammatory syndrome in children (MIS-C) is a rare complication after infection with Coronavirus disease 2019 (COVID-19), and the differential diagnosis from Kawasaki disease is predominantly based on patients' older age and positive anti-SARS-CoV-2 antibodies in most cases., Case Description: We report an "atypical" case of MIS-C in a 3.5-year-old child, with relatively low levels of inflammatory markers, persistent hyponatremia, and hypoalbuminemia, along with exceptionally high levels of brain natriuretic peptide (BNP) and myocardial dysfunction. Persistent hyponatremia was mainly related to natriuresis, while BNP elevation was a marker of the disease severity, reflecting abnormal cardiac function., Conclusion: Low inflammatory markers in children under the age of five years should not exclude a possible diagnosis of MIS-C. HIPPOKRATIA 2022, 26 (2):83-85., Competing Interests: Authors declare no conflict of interest., (Copyright 2022, Hippokratio General Hospital of Thessaloniki.)