There are no physical examination findings or laboratory tests specific to the diagnosis of premenstrual syndrome (PMS). However, physicians may take a number of steps to determine whether an underlying medical condition may be causing symptoms. Conditions that may mimic PMS include depression, anxiety disorders, thyroid disorders and perimenopause (the period leading up to menopause). In addition, a number of conditions may worsen before menstruation and mimic the symptoms of PMS. These include migraines, chronic fatigue syndrome and irritable bowel syndrome. If no such condition is found, PMS may be suspected.

To rule out other potential causes of symptoms, the physician will first take a complete medical history, including menstrual history, a list of current symptoms and any medications being taken. The physician will then perform a gynecological examination, including a pelvic examination and a Pap smear (to test for cancerous or precancerous tissue in the cervix). Additional tests will vary according to the type and severity of symptoms.

If a patient does not have an underlying medical condition that explains the presence of symptoms, PMS may be suspected. The physician may recommend the patient keep a menstrual diary to document both physical and emotional/behavioral symptoms over time.

The diary enables patients to identify symptoms and determine when they occur during the menstrual cycle. It is kept over several months to identify patterns in symptoms. If symptoms occur consistently around ovulation and last until the menstruation flow begins, then PMS is usually diagnosed. The presence of the symptoms during the first half of the menstrual cycle, however, often indicates that they are being caused by another condition.