Suzanne DeChillo/The New York Times

Ann Logan and her three sisters grew up in Delaware; none of them have children. Their stepbrother and seven first cousins on both sides are childless, as well. “Each of us had different reasons,” she told me.

Ms. Logan, the eldest sister at 63, doesn’t regret her decision not to be a parent, but she does worry about the future as she and her relatives all age.

For now, divorced and living in Manhattan, she’s a busy lawyer with good friends, caring neighbors and an Abyssinian cat named Henry. When she needed a double knee replacement a couple of years ago, a friend flew in from Fort Worth to help her, followed by another friend from Washington, followed by one of her sisters. Then neighbors came by to be sure Ms. Logan was taking her medications and to encourage her to get up and walk.

Still, Ms. Logan said, “If I have to go to an emergency room in the middle of the night, I don’t have anyone to call.”

And as the years pass, she fears her problems will mount; after all, most seniors eventually develop both chronic diseases and disabilities. “You cannot impose on the kindness of strangers endlessly, despite what Blanche said,” Ms. Logan said. (You can tell she’s a theatergoer.)

Moreover, the “chosen family” of friends that she and so many other single people rely on for support and connection will age along with her. “When there’s no one to monitor whether we’re starting to act foolishly, what happens?” she wondered. “Our contemporaries might think we’re normal because they’re having the same problems.”

How childless adults should approach their later years is a question that surfaces with some frequency among readers and commenters here. It’s true, as many attest, that being a parent doesn’t guarantee elder care. But it’s also true that the bulk of America’s old people are, in fact, cared for primarily by relatives: spouses first, then adult children.

“Children are a good insurance policy,” said Merril Silverstein, a prominent gerontologist at the University of Southern California. “In some other countries, that’s why people have children. Here, though it’s less certain, it’s still a pretty good bet.”

For Ms. Logan and others in her situation, the research on childlessness should bring both angst and comfort. For starters, seniors without children do have higher rates of institutionalization. Historically, childlessness “has been a consistent predictor of whether you end up in a nursing home,” Dr. Silverstein said.

It shouldn’t be that way, argued Debra Umberson, a sociologist at the University of Texas at Austin, who has written about childlessness and parenthood: “We shouldn’t have to have kids who work for us for free so we don’t have to go to a nursing home.”

Yet when Dr. Silverstein and fellow researchers at U.S.C. looked at a national sample of people over age 75 who had trouble walking across a room or getting in and out of bed, they found that those who were childless weren’t receiving less care than those who were parents. Nor did they score lower on measures of psychological well-being.

“The popular idea was that without children, you’d be in a whole heap of trouble,” Dr. Silverstein said. “But there’s not a whole lot of empirical evidence showing that.” Even among those childless and unmarried, “we didn’t see any indication that their unmet need was higher.”

In fact, in the national sample — which comprised 2,048 observations of 1,456 respondents from 1998 to 2004 — nearly 90 percent reported being happy and enjoying life. Among non-parents, this “positive affect” was higher still.

So it’s a mixed picture, and it’s likely to change again for baby boomers, who have much higher rates of childlessness. In the U.S.C. sample, about 14 percent were childless. Among boomers, Dr. Silverstein estimates that 20 to 25 percent are not parents (some estimates run higher), and they’re more likely to be childless voluntarily. They may have other sources of care in old age: more developed social networks, for example, or better access to paid caregivers, as women have become better educated and earned more.

“The boomers will be so different in so many ways, it’s hard to project,” Dr. Silverstein said.

Ms. Logan and her childless friends talk about their futures a lot, debating how to handle daily life in 15 or 20 years and how to cope with emergencies. “I have a horror of all the things that could happen if I didn’t plan,” she said.

So she has planned, meticulously. A federal retiree now in state government, she moved to New York specifically because it offered good public transit, inexpensive cultural activities and good health care. “I wouldn’t want to be in the suburbs or out in the country if I couldn’t drive,” she explained.

She has all her legal documents in place; friends will serve as her health care proxy and have power of attorney. She has bought long-term care insurance and kept her federal health insurance in force to supplement Medicare once she’s eligible. She has arranged for automatic bill payments so that if she’s in a hospital, the electricity doesn’t get turned off. Conscious of potential mobility issues down the road, she’s learned to order groceries online and download books to her Kindle. Her will provides for charitable bequests and income for her sisters. She has even arranged for custody of Henry.

“I know I’ve covered more things than most people,” she said. True enough, and a smart example for the rest of us, childless or not.

But the anxiety lingers. “If you don’t have someone who has strong ties to you, who is younger enough to be alert, at some point you are subject to whatever happens,” Ms. Logan said. “I’m doing what I can to avoid that, but I have no confidence that I can prevent it.”