Previous studies have shown that a third generation in a family may influence relationships between adult children and their parents. However, there is a lack of studies investigating whether being a parent is associated with relationship quality between adult siblings. Using the Generational Transmissions in Finland survey (n = 1530 younger and middle-aged adults), we investigate whether parenthood status is associated with sibling relationship quality measured by contact frequency, emotional closeness and degree of conflict. We found that mothers reported more contact with sisters with children compared to childless women with childless sisters. Fathers with childless sisters reported more contact than childless men with childless sisters. In contrast, childless men with brothers with children reported less contact than childless men with childless brothers. The results are discussed with reference to life course, shared reproductive interests, kin keeper and matrilateral effect perspectives