This commentary discusses a paper by Romundstad and colleagues, who aimed to determine whether the adverse affects associated with assisted reproduction are a result of the technology or couples' infertility. The study used data from the Medical Birth Registry of Norway from January 1984 to June 2006, and analyzed the outcomes of the whole population, and of sibling pairs where one sibling was conceived by assisted reproduction, and the other by spontaneous conception. The study showed that in the whole population, babies conceived via assisted reproduction experienced more adverse events than babies conceived via spontaneous conception. Among the sibling pairs, however, assisted reproduction was not associated with increased risk of low birth weight, premature delivery, small size for gestational age, or perinatal mortality. The results indicate that the adverse outcomes associated with assisted fertilization could be attributable to factors that lead to infertility and subfertility, rather than the reproductive technology. Follow-up studies should be performed to identify genes or other factors that lead to high risks of adverse events among subfertile couples, and these couples should be counselled about the increased risk of adverse events during and after pregnancies.