Conversion to in-vitro fertilization (IVF) and embryo transfer as an alternative to cancellation was offered in 27 consecutive cycles of controlled ovarian hyperstimulation and intra-uterine insemination (IUI) cycles with excessive follicular development in patients with idiopathic infertility. IVF and embryo transfer was performed in 25 cycles, resulting in 13 pregnancies (52%), with 22% of couples having at least two embryos cryopreserved. The pregnancies have resulted in one singleton and two twin births, one spontaneous abortion, and nine ongoing pregnancies (including one triplet gestation). Four patients developed severe ovarian hyperstimulation syndrome (OHSS) after IVF and embryo transfer, including two cases requiring paracentesis. Three of four OHSS patients were pregnant, resulting in live births of healthy twins, one spontaneous abortion and one ongoing singleton gestation. In two cycles a spontaneous luteinizing hormone (LH) surge occurred, preventing oocyte retrieval. For these two women, drainage of all follicles except the five most likely to fertilize (18-22 mm diameter) was performed, followed by IUI, with no pregnancies or OHSS observed. Conversion of patients from IUI cycles to IVF/embryo transfer cycles avoids cancellation of the very cycles with the best chance of achieving pregnancy. OHSS remains a problem, necessitating extensive pre-IVF counselling and post-transfer vigilance.