Premenstrual Syndrome (PMS) is very old, common, and panhuman. Definitions and diagnostic methods vary greatly, and proximate etiological research has thus far been unfruitful (Connolly, 2001). Reiber (2007) recently published an evolutionary model in which PMS is hypothesized to be a byproduct of adaptations that maximize chances of mating and fertilization during the follicular phase of the cycle. This suggests that how a woman feels during the follicular phase of the cycle should be predictable by evolutionarily relevant variables related to reproduction, such as age, parity, and resources. Two hundred fifteen participants completed self-report biographical and medical questionnaires at screening, then prospectively rated 17 symptoms of PMS on a daily basis throughout the cycle. For 14 of the 17 symptoms recorded, mean follicular-week symptom severity was statistically significantly predicted by age, parity, and resources. Total symptom load during the follicular week was significantly negatively correlated with age and resources, and positively correlated with parity. Women meeting diagnostic criteria for PMS had significantly lower total symptom loads (that is, they felt better) during the follicular week of the cycle than did women without PMS. This suggests that women have PMS not because something negative happens with the approach of the premenstruum, but rather because evolutionarily adaptive positive states are fostered during the follicular phase of the cycle for some women. This conceptual shift may lead to improvement in definitional and diagnostic approaches, more fruitful proximate research, and better clinical treatment.