Introduction Fever of unknown origin is an important diagnostic challenge. Although rare, periodic fever syndromes may often present with a chronic or recurrent febrile condition with a variable temporal pattern of occurrence. Although clinical characteristics often indicate the syndrome in question, there are many atypical forms, and the genotype-phenotype relationship is highly complex, warranting in many cases the designation of a "syndrome spectrum" rather than a syndrome per se. The aim of this paper was to present a boy with recurrent fever of unknown origin. Case outline We hereby present a boy with recurrent fever of unknown origin who was by clinically guided partial exome sequencing found to have a heterozygous variant 434A>G in the TNFRSF1A gene, otherwise connected with tumor necrosis factor receptor-associated periodic fever syndrome. The patient responded well to short courses of glucocorticoids and is no longer subjected to unnecessary antibiotic treatment he had frequently received in the past. Conclusion Periodic fever syndromes should be kept in mind as a differential diagnostic possibility in children with fever of unknown origin.

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