Objective: This research's primary objective was to classify the occurrence of hypothyroidism in patients with major β-thalassemia. Place and duration of study: This research was performed from July 2020 to February 2021 in the Pediatrics Department of FMDC Islamabad for eight months. Study Design: It is a type of cross-sectional research. Sampling Technique: Consecutive sampling method with non-probability Material and Methods: A total of 75 patients with major β-thalassemia were chosen for this study. The maximum age was 5-15 years. The selection of patients was random from either sex. A sample of 3 ml of blood was delivered to a reputable laboratory to determine the TSH and T4 level. The ELISA package, to test the level of TSH and T4 level, was used. This data was analyzed to determine the incidence and percentage of hypothyroidism using SPSS version 20. Informed consent and ethical approval were obtained from patient families and hospital committees, respectively. Inclusion criteria: Cases of confirmed beta-Thalassemia major Between 5 and 15 years of age groups for either sex. Exclusion criteria: Acute Illness Patients, Patients with minor and intermediate thalassemia. Results: Hypothyroidism was observed in the children having an average age of 10.48±2.6 years. A total of 22 patients were suffering from hypothyroidism (29.3 percent). Of these, eight patients (30.8%) were female, and 14 (28.6%) were male. Conclusion: Children with β thalassemia major can also suffer from hypothyroidism, even in the absence of signs and symptoms. It is also essential to routinely screen children with beta-thalassemia for hypothyroidism to allow an early diagnosis and provide immediate care. Keywords: Hypothyroidism, β thalassemia major, TSH, T4.