Background: Thyroid disorders have been implicated in a broad spectrum of 'reproductive disorders ranging from abnormal sexual development to menstrual irregularities and infertilityllypo and hyper thyroidism may have an important impact on cycle length and amount of bleeding. Objective: Elle current study aims at studing the prevalence of thyroid dysfunction in female patients presenting with secondary infertility compared to an age-matched population. Design: Case controlled study. Setting: King Khal id Military City Hospital. Material: 120 Selected patients presenting with secondary infertility with a mean age of 28.2+1-5.1 year with no known or clinically evident thyroid disease were included. 40 Age-matched fertile females served as controls. Methods: Patients and controls were subjected to the study of: • Serum TSH by ultrasensitive test • Serum Free T3 • Serum Free T4 Results: • 14/120 (11.6%) patients had evident thyroid dysfunction compared to 1/40 of (2.5%) the control group [p