Due to increasing number of cases of thyroid gland disorders nowadays, there are rising trends of thyroid gland surgeries and interventions which requires comprehensive data regarding the gland. This study was done to find out the changes in the size of the thyroid follicle in different age groups. The age groups were Group A - upto 20 years, Group B – 21-50 years and Group C – above 50 years. The study was conducted on 60 human thyroid glands in the Department of Anatomy in collaboration with Department of Pathology, Pt. B. D. Sharma Post Graduate Institute of Medical Sciences, Rohtak in North Indian population. The diameter of the thyroid follicle was measured by Image Analyzer. The study revealed that the mean size of the thyroid follicle was found to be in Group A - 56.38±14.12 μm, Group B - 130.08±30.67 μm and Group C - 96.05±12.86 μm. The study concluded that the mean size of the thyroid follicle was found to be higher in Group B (21-50 years) followed by Group C (above 50 years) followed by Group A (below 20 years).