Aim of this study was to assess the efficacy of recombinant luteinizing hormone (rLH) supplementation in late follicular phase in multiple follicular stimulation with recombinant follicle stimulating hormone (rFSH) in Triptoreline down-regulated patients undergoing IVF, on preventing clinical OHSS and cycles cancellation for OHSS risk. Nine hundred ninety-nine patients aged ≤ 40 with basal FSH ≤ 12 mUI/Ml were down-regulated before starting rFSH stimulation for oocytes recovery. Patients were allocated in two groups: (A) (501 patients) treated with 150 IU of rFSH eventually adjusting rFSH dosage day 7 of stimulation until recombinant human chorionic gonadotropin (rhCG) administration, (B) (498 patients) treated with 150 IU of rFSH and 75 IU of rLH since day 7 of stimulation until rhCG administration and adjusting rFSH at the same day. E2 the day of rhCG was higher in group B (p < 0.0001); number of cycles cancelled in group A (42/8.3%) for risk of ovarian hyperstimulation syndrome (OHSS) was higher than group B (12/2.4%) (p < 0.000001). We observed an increase in pregnancies in group B compared with group A (16.8% vs 11.9%) (p < 0.05) and we observed also a larger number of clinical OHSS in group A than in group B (p < 0.05).