Transfusion dependent thalassemia (TDT) patients require a regular blood transfusion to survive. Without adequate transfusion support, they suffer many complications, and have a short life span. Near about 200 milligrams of iron remains within a single Red cell concentrate (RCC) unit. So, blood transfusion acts as a double-edged sword, prolonging life while eventually leading to iron overload. For patients who are receiving transfusions for several years, iron accumulation causes different types of morbidity including thyroid failure. Though serum ferritin is a simple tool for measuring the iron load of the body, it is often misleading. Because, in first 100 unit of blood transfusion serum ferritin levels increase steadily. After that, this relation is not simple. Serum ferritin may increase in chronic inflammation or decrease in vitamin C deficiency, which may be misleading. The study aimed to identify a simple predictor of hypothyroidism in TDT patients. This cross-sectional study conducted from April 2018 to September 2019 includes 64 TDT patients according to selection criteria. Among them 43 were male and 21 were female TDT patients, with a mean age of 25.5 years. Body iron load was estimated by serum ferritin level. Pearson correlation test was done to measure the correlation of serum TSH level with serum ferritin, unit of blood transfused so far and duration of receiving transfusion therapy. All of these three variables had positive correlation with serum TSH level (r value 0.241, 0.319 and 0.332 respectively). Level of correlation of serum TSH was statistically significant with unit of blood transfused (p=0.010) and with duration of transfusion therapy taken (p=0.007) but not with serum ferritin level (p=0.055). Meticulous transfusion history taking is more important than investigation reports like serum ferritin level to predict hypothyroidism in TDT patients.