I must have been 12 years old when my mother took me aside to tell me she had been married to another man before my father. I was stunned, shocked and, yes, ashamed.

In these days of multiple marriages and blended families, I can't even say why exactly I was ashamed. There was nothing to be ashamed of, even then.

My mother's mother had died, and within the year, both her father and brother married. Feeling alone, she married, too.

In retrospect, I think I was ashamed because she was. The proof of the shame was the secrecy.

If there was nothing to be ashamed of, why keep it secret for so many years? Why invent tales of a white wedding when, I later learned, the black-and-white photos didn't show that it was really a cream-colored dress?

My mother explained that she told me because she was afraid a stray comment by someone might reach my sister and me. That happened in the case of a friend with a much bigger family secret: She had a sister she didn't know about.

Another friend's father, who had something to do with finding a placement for the child, said something to his daughter, not knowing the sister was a secret. One thing led to another, and we knew before the sisters did.

There are secrets that must be kept. As a lawyer, I'm in the business of keeping secrets, and my ability to assure my clients that they can speak freely is, frankly, what allows me to do my job.

But secrets in families more often have just the opposite effect. They get in the way of true family, covering with shame the very relationships that need to be nourished with honesty.

In his wonderful book "Annie's Ghosts: A Journey into a Family's Secret," veteran journalist Steve Luxenberg unearths the secret his now deceased mother never shared with her children.

She was not, as she told her children and anyone else who asked, "an only child." In fact, she had a sister, Annie - a sister she grew up with, a sister who shared her childhood, a younger sister who was institutionalized just short of her 21st birthday, when her screaming through the night was pushing her family to despair.

Annie was not only a daughter, but also a sister and an aunt, roles she was denied in the desperate effort of Steve's mother to avoid the shame and stigma of a mentally ill and handicapped sibling.

In moving and honest detail, Steve recounts the search he embarked on after his mother's death to uncover the mystery of his missing aunt, all the while trying to understand how and why his mother kept her a secret. In the process of doing so, he is forced to reexamine how that secret isolated his mother; how it put walls between her and her own children; how it changed his view of the mother he adored.

Parents keep secrets from their children in the hopes of protecting them, but almost always, it does just the opposite. We protect our children by teaching them how to deal with adversity, not by hiding it. We teach them humanity not by walling off what is painful, but by confronting it with compassion.

A few years before she died, Steve's mother was diagnosed with severe depression, which, coupled with her emphysema, required her to undergo a brief period of hospitalization in a psychiatric hospital to monitor her adjustment to new medication.

Steve recounts in detail his mother's terror at the hospitalization, her screaming in the night and his inability to understand her fear, much less reassure her. Only after learning about what happened to Annie did he understand what must have been his mother's unspeakable terror that she was becoming her sister.

The secret stood in the way of the understanding and love her children would have so gladly given to her. It usually does.

Examiner columnist Susan Estrich is nationally syndicated by Creators Syndicate.