Prolactinomas, tumors that produce prolactin (PRL), are one of the most frequent pituitary tumors and the main cause of pathological hyperprolactinemia. These tumors are more frequently diagnosed in women and usually affect the reproductive axis, leading to secondary hypogonadism. The diagnosis of prolactinoma is based on the presence of clinical features -- such as menstrual irregularity, erectile dysfunction, galactorrhea, and infertility -- and the detection of elevated serum PRL levels and confirmed by the existence of a pituitary tumor on magnetic resonance imaging. This book discusses the relation between prolactinomas and the increase in body fat and weight.