PMS is an ill-defined group of symptoms that are associated with the hormonal changes that occur in the week or so prior to menses. When severe, the personality and anti-social behavior associated with PMS could be a definite problem in diver interaction on a dive-boat and with a buddy. If the PMS is severe, there seems to be an association with underlying psychiatric disorders. It also worsens as the diver ages, associated with the widening range of estrogen swings. Hormonal replacement works well with PMS. SSRI’s have been found beneficial.