The authors' first study compared participants' relationships between their siblings with and without a developmental disability (DD) and examined the effect of gender on sibling relationships. The second study explored how adults with a DD perceived their sibling relationships. Adults (n = 128) who had a sibling with and without a DD completed questionnaires about relationship closeness and contact. Participants reported more in-person and telephone contact with siblings with a DD and more positive feelings about the sibling relationship. Gender was not related to the relationship with a sibling with a DD, whereas sisters reported closer relationships and more contact with sisters without a DD as compared to brothers without a DD. Seventeen adults with a DD also completed interviews about shared activities, contact, and sibling support. Participants indicated a desire to spend more time with siblings and reported that they provided support to and received support from their siblings.