The aim of the present study was to determine a possible relationship between ovarian functionality and regression of ovarian enlargement according to the different categories and degree of severity of ovarian hyperstimulation syndrome (OHSS). Among a group of sterile woman (n = 111), two subgroups were studied: group A (n = 15), patients affected by severe syndrome; and group B (n = 96), patients with massive ovarian enlargement only. The protocol of ovarian stimulation was conducted in various in vitro fertilization (IVF) centers; ultrasonographic examination and hematological checks were carried out daily; patients with severe OHSS were hospitalized. In women of group A, severe symptoms disappeared in 7-11 days; in nine patients with regular cycles ovary size returned to normal in about 30-40 days, whereas in six subjects with anovulatory cycles, the resolution was recorded in about 50-60 days; serum estradiol returned to physiological levels within 20-30 days. Women of group B showed a spontaneous regression at different times: in 43 subjects that presented regular ovulatory cycles, the resolution was recorded in about 30-40 days, whereas in 36 women with anovulatory cycles before pharmacological induction, resolution occurred in 50-60 days, and in 17 cases with polycystic ovary syndrome before pharmacological ovulation, an incomplete resolution was obtained; serum estradiol levels returned to a physiological range within 20-30 days. Our results show that in patients with regular ovulatory cycles, resolution of symptoms is obtained in a shorter time than in patients with anovulatory cycles before pharmacological induction.