Introduction: Hypothyroidism is a silent epidemic of our times. In India, the prevalence of hypothyroidism is 11%. The effect of hypothyroidism on respiratory system is debatable with studies suggesting both obstructive and restrictive disease patterns. The symptoms range from mild dyspnoea to life-threatening respiratory failure. This study emphasizes the effect of hypothyroidism on dynamic respiratory functions. Aim: To find out the changes in dynamic respiratory functions (FVC, FEV1, FEV1% and PEFR) in both male and female hypothyroid patients within age group of 18-45 years. Materials and Methods: This cross-sectional study was conducted in Jubilee Mission Medical College, Thrissur, Kerala, India. Total number of 60 newly detected cases of both sexes in 18-45 years age group attending endocrinology outpatient department were enrolled. Patients with previous respiratory diseases and history of smoking were excluded. Proforma was filled up followed by clinical examination. Spirometry was performed using a computerised spirometer` microQuark'. The data was analysed by paired t-test and Analysis of Variance (ANOVA) test. Results: The mean of the observed values in all the dynamic pulmonary parameters showed highly significant difference from the predicted mean of the parameters (p< 0.001). They also decreased considerably with age, gender and BMI which were statistically significant (p< 0.05). Conclusion: The above findings suggest that respiratory abnormality in newly detected cases of hypothyroidism shows a mixed pattern. This highlights that while investigating a patient with respiratory disorder, the thyroid status should always be probed into, as the effects of hypothyroidism can be reversed with proper treatment.