Abstract
Studies have established that having older brothers is associated with an increased incidence of male homosexuality. This so-called fraternal birth order effect has been found in different times and cultural settings. The current study attempted to examine whether this effect was present in the Greek cultural context and whether it could also predict bisexuality or heterosexuality with occasional same-sex attractions. On the basis of an online sample of 1617 Greek-speaking participants, it was found that, for men, a higher number of older brothers were associated with an increased probability to be homosexual, but it had no effect on the probability to be bisexual or heterosexual with same-sex attractions. In women, the number of older brothers had not any effect on sexual orientation.