This study examined the effects of sibling relationships and relationships with friends on loneliness amongst young and middle aged adults. The results reveal that women have more warmth with siblings than men and young adults experienced more conflict than middle aged adults. In addition, men experienced more conflict with friends than women and young adults had more warmth and experienced more conflict than middle aged adults. The warmth of both siblings and friends correlated negatively with social, romantic and family loneliness and patterns of conflict appeared somewhat different in young and middle aged adults. Relationships with friends had greater effects on social loneliness than romantic and family loneliness, and sibling relationships had greater effects on family loneliness than other forms of loneliness. Additionally, sibling relationships among young adult males had greater effects on romantic loneliness than other forms of loneliness, and among young adult females, relationships with siblings and friends had greater effects on romantic loneliness than romantic and family loneliness. Relationships with friends among middle aged adults had greater effects on romantic loneliness than other forms.