Not likely. But in times past -- sometimes not so distant -- that was the mechanism some couples chose to establish a legally recognized relationship. A few appellate court opinions on the subject have made it into family law textbooks. New York ruled famously in the 1980's that such an adoption violated the state's public policy. But many states allow it. Interestingly, two different Florida judges told me in the 1990's that they had granted such adoptions.
Gay rights lawyers have pretty uniformly discouraged such proceedings. You can't divorce your adopted child/parent. You probably have to present yourselves to the court in a manner that is dishonest. But they still happen.
The most recent example to come to public attention is the adoption of Patricia Spado by her then partner Olive Watson. The case has gotten lots of press coverage because Spado stands to inherit oodles of money pursuant to a trust established by Thomas Watson Jr, the son of the founder of IBM. The trustees have been trying to undo the adoption, and they just lost in the Maine Supreme Court. If you don't want to read the court's whole opinion here, you can read Professor Art Leonard's fine summary. Basically, Maine law allowed such adoptions at the time (not anymore), and the court found that the parties satisfied the jurisdictional requirements under Maine adoption law even though they only spent summers there.
Inheritance was actually a major reason for adult adoption...dating back to antiquity. For gay couples, an adoption could prevent a deceased partner's family from challenging a will leaving property to the surviving partner. After all, if the will was thrown out the property would go to a surviving child before going to siblings or more distant relatives.
The gay partner adoption I think about most often is that of Robert Allerton's adoption of John Gregg (whose name became John Gregg Allerton). I came across their story by accident. I was touring the Allerton gardens on Kauai in the early 1990's. Early on the tour guide referred to "Robert Allerton and his adopted son..." Now I am an adoptive mother. I have friends who are adoptive parents and friends who are adopted. It struck me as unusual to have these two individuals described this way; normally, a person would say, "Robert Allerton and his son..." So my ears perked up.
As the tour went on, I learned about how the couple travelled the world collecting art for the garden; how they created "rooms" and had costume balls. Okay, so it was clear to me they were a gay couple. They met in the 1930's and were together until Robert's death in 1964. Robert, an heir to one of Chicago's greatest fortunes, adopted John in Illinois in 1951. I returned home and regaled my friends with stories of finding gay family law history so unexpectedly. (We are everywhere, right?)
On that tour I didn't ask any direct questions. But the gardens are stunning and Kauai is my favorite place in the world, and I returned there a couple of years later. In response to my questions, the guide told me then that it was commonly assumed they were a couple and that everyone in Kauai society attended the parties they gave in their gardens. "We don't care," she said. "We are just grateful they left this property for us." The official history on the Allerton Gardens website speaks of the couple's life and travels, and says that Robert adopted John. Anyone even remotely in the know can read between the lines.
I dug around a bit and thought about writing an article on the Allertons and their garden for a travel magazine with a gay focus (or a gay publication with a travel section?). I never did. In the September 2007 issue of Out, Bruce Shenitz did write such an article, entitled The Garden of Eden. Minus Eve.
Oh, and if you make it to Kauai, visit these gardens. They are stunning. And imagine the lives of the two men who called this place home and what those lives would have been like had they lived 50 years later.