Thyroid dysfunction is relatively common in women, particularly in the reproductive ages. Because thyroid problems may cause changes in menstrual bleeding, infertility, or abnormal findings during annual gynecologic screening, the obstetrician-gynecologist often may be the primary physician involved both in the initial evaluation and in therapy. An accurate evaluation of the patient's medical problems and hence, diagnosis of thyroid dysfunction is dependent on an understanding of normal thyroid physiology, the symptoms of thyroid disease, and the various laboratory tests that demonstrate the presence or absence of normal thyroid function. In particular, TSH and free T4 levels allow the diagnosis of the most common causes of hyper- or hypofunctioning of the thyroid gland, including Graves' disease, Hashimoto's disease, and toxic nodular goiter. Recommendations regarding screening guidelines, approach to diagnosis, and management or patient referral are presented in the context of the common thyroid pathologies. © 1994.