The aim of this retrospective study was to investigate factors affecting clinical pregnancy rates, especially age and duration of embryo transfer, in IVF/intracytoplasmic sperm injection cycles (11313 embryo transfers). Overall clinical pregnancy rate was 30.0% (n = 394). Clinical pregnancy rates were found to be 31.6% for the <44 s interval, 25.9% for the 45-59 s interval and 23.6% for the >60 s interval (P = 0.020). In the <35 year age group, clinical pregnancy rates were 35.1%, 29.9% and 30.6%, and in the >35 year age group, they were 26.9%, 21.0% and 13.4% (P = 0.013), respectively. According to logistic regression analyses, the odds of failed pregnancy increased by 1.61 times [95% confidence interval (CI) 1.07-2.41] for embryo transfer durations longer than 60 s and odds ratios of a failed pregnancy were 1.53 (95% CI 1.18-1.99) in the >35 year age group, 1.49 (95% CI 1.05-2.12) for fewer than five oocytes and 3.38 (95% CI 2.10-5.43) for fewer than two transferred embryos. In conclusion, to increase the likelihood of a successful pregnancy in women over 35 years of age, the duration of embryo transfer must be kept below 60 s. The number of oocytes obtained and the number of transferred embryos also play a role in the success of pregnancy. (C) 2009, Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.