Details of 767 clinical pregnancies and 500 births from Bourn Hall are reported. All treated patients included some over 40 years old, many with ovarian or uterine defects, male infertility, etc. Patients were treated during their natural cycle or stimulated with clomiphene or clomiphene and human menopausal gonadotrophin. Follkular maturation was induced by an endogenous luteininng hormone surge or human chorionk gonadotrophin. A maximum of three embryos were replaced, except in a few patients receiving four. Twenty-eight percent of pregnancies aborted, occurring more frequently in patients who were over 40, with a complicated obstetric history, and given clomiphene alone. Approximately 18% of fetuses ‘vanished’ in multi-pregnancies. Seventy-one sets of binovular twins and nine sets of triplets have been born, and seven twins and three triplets are ongoing. Seventeen and a half per cent of patients aged 39 and less with one or more replaced embryos delivered one or more children, rising to almost 25% with three replaced embryos. A mean of 1.3 children were born per delivery when three embryos were replaced. Most deliveries were by Caesarean section. There were two cases of placenta praevia, one stillbirth, four major and eight minor anomalies. All the triplets, and some twins and singletons had low birth weights and were born prematurely. The sex ratio was 247 males to 253 females.