- Unlabelled: Periodic fever of childhood is a group of diseases that cause repeated febrile illnesses with various associated symptoms. In our article, we present the case of a 6-year-old girl with unusual appearance of periodic fever syndrome. Our patient suffered from repeated episodes of high fever from the age of 2 years old. Each episode usually lasted 24-48 h, the interval between events was 1-3 weeks long. During high fever episodes the child usually felt well, without associated accompanying complaints. As a rule, the physical examination did not reveal any pathologic finding explaining the fever. During the 4 years of follow-up the patient sustained treatment attempts with prednisone for a number of months and half a year with colchicine without any response. We considered treatment with sublingual tablets of vitamin B12 (VIT B12). Beyond all expectation, we witnessed complete resolution of attacks during the first 2 months following treatment. After a long episode-free period, the parents withheld the treatment on their own accord, and in a short time the disease recurred. We advised to renew the treatment with VIT B12, and during approximately half year of follow-up there were no recurrences of periodic fever. Conclusion: we believe that our observation raises interest in systematic evaluation of the therapeutic role of VIT B12 as a treatment option for disorders of the periodic fever spectrum.