Your sister might steal your clothes and makeup, and just generally get on your nerves, but according to research, having her in your life makes you a happier person.
The study by De Montfort University and Ulster University found that sisters encourage each other to talk about their feelings, which leads to having a better, more happier, mood.
"Sisters appear to encourage more open communication and cohesion in families," Professor Tony Cassidy explained.
However, the finds weren't as great for those with brothers.
"Brothers seem to have the alternative effect," Professor Cassidy said. "Emotional expression is fundamental to good psychological health and having sisters promotes this in families.
"It could be that boys have a natural tendency not to talk about things. With boys together it is about a conspiracy of silence not to talk. Girls tend to break that down".
Of course, it is important to remember that this is just one study which only surveyed 571 people between 17 and 25.