Objectives: To describe the clinical and epidemiological characteristics of children with fever of unknown origin (FUO) at the National Institute of Child Health in Lima, Peru. Material and methods: Descriptive and retrospective study with 100 patients younger than 17 years of age, hospitalized between 2006 and 2010. FUO was based on the following criteria: fever > 38.3 oC, with an evolution ≥ 3 weeks, without established cause, or febrile patient without diagnosis etiology after three days of hospitalization. Clinical records were reviewed, obtaining personal history and physical examination data, as well as laboratory and imaging findings. Results: Of the total, 49% were under two years of age. An infectious disease was the most frequent cause of FUO (48%), followed by neoplasms (6%), and 2% due to other causes. In 44% no specific diagnosis was reached. Cat scratch disease (8%) was the main infectious etiology, followed by urinary tract infection (7%). Regarding neoplasms, five patients had leukemia and one histiocytosis. Conclusions: In pediatric patients with FUO, infectious aetiology was the most frequent cause, followed by neoplastic disease. There is a high percentage of patients with FUO in whom its etiology cannot be determined.