Premenstrual syndrome (PMS) is a condition that affects a woman's emotions, physical health, and behavior during certain days of the menstrual cycle, generally just before her menses. PMS is a very common condition. Its symptoms affect more than 90 percent of menstruating women. It must impair some aspects of your life for your doctor to diagnose you. PMS symptoms start five to 11 days before menstruation and typically go away once menstruation begins. The cause of PMS is unknown. However, many researchers believe that it's related to a change in both sex hormone and serotonin levels at the beginning of the menstrual cycle. Levels of estrogen and progesterone increase during certain times of the month. An increase in these hormones can cause mood swings, anxiety, and irritability. Ovarian steroids also modulate activity in parts of your brain associated with premenstrual symptoms. This is a book about medicine and the history of a condition called premenstrual syndrome (PMS), its "discovery" and conceptual development at both scientific and socio-cultural levels. Since it was first mentioned in medical literature, PMS has been explored empirically as a medical condition and conceptually as a non-somatic cultural phenomenon. Many attempts have been made to produce scientific, empirical evidence to bolster the theory of PMS as a biological disease. Some non-medical perspectives argue that invoking biology as the cause of PMS medicalizes a natural function of the female reproductive system and shallowly interrogates what is a complex bio-psycho-social phenomenon. This thesis questions both sides of this debate to reveal how criteria for PMS were categorized despite disagreement surrounding its etiology. This thesis illustrates how the concept of PMS developed and was informed by the discovery of hormones and the resulting field of endocrinology that provided a framework for conceptualizing PMS. It displays how the development of the medical diagnostic category of PMS developed in tandem with the emergence of the field of endocrinology and was legitimized and effectively medicalized through this connection. The diagnosis of PMS became established through diagnostic techniques like questionnaires despite persistent disagreement over its definition. The thesis shows how these medical concepts and practices legitimated the category of PMS, and how it has become ubiquitous in contemporary culture.