When Vicki Sussman was growing up, her dad was explosive, her mom let emotions fester inside and her older brother would hit her with little provocation, she says.
As an adult, says Ms. Sussman, now a university administrator in Cleveland, she rarely spoke to her brother. Then, as they neared middle age a few years ago, she and her two siblings decided to deal with their family's anger-management issues.
So they booked a weekend of adult sibling therapy.
Working with a family therapist, they spent three days doing art exercises, talking about their parents and charting out the dysfunctions in their family tree. "It was completely exhausting," Ms. Sussman says.
But during the session, she realized that all three children had suffered neglect, and that her brother's hostility was an attempt to get their parents' attention, she says.
Ever since that weekend four years ago, she adds, "my anger towards him really feels resolved."
Sibling rivalry has been around since Cain and Abel. Experts say it's particularly intense when siblings are of the same gender and close in age - such as the Corleone brothers' lethal rift in The Godfather or the tennis-court competition between Venus and Serena Williams.
But the urge to reconcile with siblings is equally strong, according to psychologists, and usually grows in adulthood. As marriages fail and close friends move away, individuals begin to realize that bonds with brothers and sisters are potentially the longest relationships of their lives.
In the past 15 years, adult siblings have become a growing area of psychological and sociological study. There's greater awareness that siblings spend more time together in childhood than they do with their parents, making siblings a major influence in a person's development.
The aging population has drawn attention to adult siblings as well. Baby boomers tend to have many brothers and sisters. And as their mothers and fathers enter nursing homes, adult siblings are seeking therapy together to heal old wounds and to strengthen their bond for the remainder of their lives.
"When the parents are gone, siblings are the only link to your childhood," explains Karen Gail Lewis, a family therapist with offices in Cincinnati, Ohio, and Washington, D.C.
The sibling relationship is the laboratory where a person learns to deal - or not deal - with issues such as conflict, rejection and affection, Dr. Lewis says.
She has offered weekend retreats for adult siblings for more than 10 years. In many cases, clients begin the therapy after issues come up in individual counselling.
For example, Dr. Lewis says, her clients' sibling relationships often parallel their romantic relationships. "Where they get stuck in a marriage is almost always where they were stuck in childhood with their siblings."
This link is based on her clinical observations and not on longitudinal studies, she notes.
Disagreements about how to care for an elderly parent is a common reason for adult siblings to enter therapy together, says Bea Mackay, a Vancouver-based psychologist.
In many cases, one child is expected to shoulder the burden while the others abdicate their responsibility. "It's often the same pattern from childhood," she says.
But siblings can help one another change their perceptions of childhood events.
"It's like they revisit history and come up with a new picture of old stuff," Dr. Mackay says. With this new picture comes the opportunity to make peace and engage together in new ways.
In a therapy session, Dr. Mackay acts as a filter to help siblings better communicate. The process is similar to marriage counselling, she says, except it doesn't take as long. "Usually we're able to get to the heart of the matter quite quickly. It's often only a few sessions."
Siblings rarely refuse to show up for one another in therapy, according to Marvin Todd, a specialist in the field and the author of Linked for Life.
"Siblings are wonderful historians for each other," he adds.
Michael Klein, Jr., an orthopedic surgeon in Sacramento, Calif., says he entered therapy to deal with depression. Then he realized there was a five- to seven-year gap in his childhood that he could barely remember.
His three adult siblings, with whom he rarely spoke, agreed to fly into Sacramento and meet with him in his therapist's office.
Dr. Klein says he spent much of the five-hour-long session listening as his brother and two sisters talked about the forgotten years of his life.
They described his father as a pathological liar and his mother as an enabler, and shared memories of being unable to rely on either parent. "It was painful for me," Dr. Klein says. "I sat there and cried."
But that one session turned their relationship around, he says. Today, he and his siblings enjoy weekly phone calls together and visit one another regularly.
"Whatever that little burning ember was among all of us," Dr. Klein says, "the sibling family therapy was a breath of fresh air that caused it to glow."