Endocrinologists specialize in glands and all the hormones they produce. Endocrinologists commonly treat diabetes, thyroid dysfunction, and reproductive health. You may see an endocrinologist for any of the above, and will usually be referred by your PCP if you report symptoms or have related discrepancies in your blood work. Some endocrinologists do focus specifically on one area of the body. For example, a reproductive endocrinologists focuses on the reproductive system, and people often work with these doctors when seeking fertility treatments.