Background and aim Anemia is a condition characterized by a deficiency in red blood cells or hemoglobin (Hb), which significantly impacts adolescent girls, often due to dietary deficiencies and lack of counseling at menarche. This research aims to find the prevalence of iron deficiency anemia (IDA) among teenage girls after menarche, and attending outpatient departments (OPDs) caused by reasons unrelated to pathological anemia. Materials and methods This cross-sectional study, conducted at a tertiary care hospital from April 2024 to November 2024, included 165 teenage girls aged 13-19 years with anemia (Hb ≤12), excluding known cases of hemolytic anemia or autoimmune disorders, recent blood loss, significant organ dysfunction, psychiatric illness, and ongoing anemia treatment. Complete blood count (CBC), serum iron, serum ferritin, and total iron-binding capacity (TIBC) were used to assess anemia. Results The age of menarche ranged from nine to 16 years, with a mean of 12.5±2.53 years. Fifty-five (33.33%) of participants had moderate anemia (Hb 8-10 g/dL) or severe anemia (Hb<8 g/dL), while 110 (66.67%) either had no anemia or mild anemia (Hb >10 g/dL). One hundred thirty-five (81.8%) were unaware of anemia prevention methods. Significant associations were found between anemia and dietary habits, heavy or irregular menstrual bleeding, supplement use, and symptoms of anemia (fatigue, dizziness, and weakness). Conclusion This study showed a high prevalence of IDA in teenage girls, particularly at menarche when iron needs increase. Vast educational plans and awareness campaigns are recommended to be implemented in society for the prevention, early diagnosis, and management of anemia in teenage girls.