This document discusses menstruation and menstrual irregularities. It begins by explaining the normal menstrual cycle and defining different types of irregularities such as amenorrhea, oligomenorrhea, and menorrhagia. It then covers evaluating a patient's history and conducting an examination. Key aspects of the history include age, medical disorders, surgery history, and family history. The examination focuses on secondary sex characteristics, systemic examination, and pelvic examination. Investigation of menstrual irregularities may include pregnancy testing, hormonal assays, ultrasound, and genetic testing. Specific conditions that can cause amenorrhea like hyperprolactinemia, Kallmann syndrome, and anorexia nervosa are also summarized.