We report for the first time increased concentrations of aldosterone and renin in a case of spontaneous, recurrent, familial, severe ovarian hyperstimulation syndrome (OHSS). High concentrations of Ca125 were also found. Our patient was a 26 year old woman, gravida 2, para 1, affected by severe OHSS, who denied having ever consumed any ovulation drug. Both the patient and her only sister had suffered from a similar condition in their previous pregnancies. The patient was treated with i.v. fluid therapy. Paracentesis was performed on one occasion. The patient was dismissed after 25 days in good condition. Blood count and blood chemistry confirmed the severity of the clinical picture. We conclude that spontaneous OHSS, although very rare, may have been underestimated so far. It can be recurrent and may also be familial. The intra-ovarian prorenin-renin-angiotensin system may play a role in its aetiopathogenesis.