Hypothyroidism is one of the most common endocrine disorders encountered in clinical practice. Thyroid disorder is very common among the female. The aim of this study was to evaluate the effects of hypothyroidism on menstrual pattern and sub-fertility. This cross-sectional comparative study was carried out in the Department of Obstetrics and Gynecology with collaboration of endocrine department of Bangabandhu Sheikh Mujib Medical University (BSMMU) from July 2006 to June 2008, cases were collected from the thyroid clinic of this hospital. Total study subject were 139, among them hypothyroid cases were 79 and euthyroid were 60. Among the hypothyroidism group 62.0% (n=49) had normal menstrual cycle, 21.5% (n=16) had oligomenorrhoea, 10.1% (n=8) had polymenorrhoea and 6.3% (n=6) had amenorrhoea. On the contrary in euthyroid group 86.7% (n=52) had normal menstrual cycle, 6.7% (n=4) had oligomenorrhoea, 5.0% (n=3) had polymenorrhoea and 1.7% (n=1) had amenorrhoea. Proportion of abnormal menstrual history was found to high among hypothyroid group almost 34% (n=27) compared to euthyroid group 13.4% (n=8) and the difference was statistically significant (p<0.001). The proportion of primary subfertility in hypothyroid 11.4% (n=9) whereas in euthyroid cases 1.7% (n=1) and secondary subfertility in hypothyroid 7.6% (n=6) where as in euthyroid cases 5.0% (n=3). So, sub-fertility was higher among hypothyroid group compared to euthyroid group but the difference was not statistically significant (p>0.05). Overall sub-fertility was 13.7% (n=10) and it was 6.7% (n=4) among the euthyroid group. Among total hypothyroid group 60.7% (n=48) are the overt hypothyroid and 39.20% (n=31) are the sub-clinical hypothyroid group. The effect of hypothyroidism is significant on menstrual pattern and on fertility. Hypothyroid women had more menstrual disorders and also suffering from sub-fertility.