Although congenital erythrocytosis (CE), an inherited disorder, impairs pediatric quality of life, physicians often overlook high hemoglobin (Hgb) levels and its symptoms due to lack of knowledge of age-adjusted pediatric Hgb levels and CE's rarity. In a retrospective, single-center study, data from hospital records of pediatric patients diagnosed with CE were evaluated. Twenty-six patients from 25 families (80.8% male) had been diagnosed with CE in 20 years, at a mean age of 14.9 +/- 2.8 years (8.3-17.8) and with a mean Hgb level of 17.36 +/- 1.44 g/dL (14.63-22.1). No serum erythropoietin levels exceeded the reference levels. Although the most common symptom was headache (85%), 38% of patients presented with at least one gastrointestinal symptom (e.g., nausea, vomiting, abdominal pain, and rectal bleeding), and 54% exhibited plethora. No patient had leukocytosis, thrombocytosis, JAK2 mutation; capillary oxygen saturation, venous blood gas analysis, and Hgb electrophoresis revealed no abnormalities. While 34.6% of patients had family histories of CE, 42.3% had 15-45-year-old relatives who had experienced myocardial infarction, stroke, and/or sudden death. Aspirin was routinely prescribed, and phlebotomy was performed when hyperviscosity symptoms were present. To detect CE, physicians should consider age-adjusted normal Hgb levels in children. Pediatric patients with CE may also present with gastrointestinal symptoms. Although no thrombotic episode occurred among the patients, their family histories included life-threatening thrombotic episodes, even in adolescents.