Objective: To compare the live birth rate, multiple pregnancy rate, and obstetric outcomes of elective single and double embryo transfers.Design: Case series with internal comparisons.Setting: University affiliated hospital, Hong Kong. Participants:Between October 2009 and December 2011, 206 women underwent their first in-vitro fertilisation cycle. Elective single embryo transfer was offered to women who were aged 35 years or below, and had endometrial thickness of 8 mm or more and at least two embryos of good quality. Main outcome measures:Live birth rate, multiple birth rate, and obstetric outcomes.Results: Among the 206 eligible women, 74 underwent an elective single embryo transfer and 132 a double embryo transfer. The live birth rate was comparable in the two groups, being 39.2% in the elective single embryo transfer group and 43.2% in the double embryo transfer group, while the multiple pregnancy rate was significantly lower in the elective single embryo transfer group than the double embryo transfer group (6.9% vs 40.4%; P<0.001). Gestational ages and birth weights were comparable in the two groups. There was no significant difference between