Downsizing can be a good thing.

Peter Theriault understands that. Streamlining his operation helped the Camden man get back into the music business.

For 25 years, Theriault was a professional musician, playing piano, synthesizer and keyboards. Sensing changes in the business, he became a gemologist, leaving music behind. Then he picked up an accordion about three years ago and found his entry back in.

“I felt there was something missing in my life,” explained Theriault, 48. “It’s satisfying to be back in the business, and to have it so well-received. It’s satisfied that part that was vacant for so many years.”

Theriault continues his public comeback this evening, as he brings his “World Music According to the Accordion” to the Custom House Cafe in Rockland. From 7 to 10 p.m., he’ll be playing world music, Parisian cafe songs, Italian, Jewish, zydeco, Tex-Mex, Cajun, Irish and American standards.

“It’s a travelogue of different tunes on the accordion,” he said.

Theriault has heard all the jokes about Lawrence Welk and polkas. His defense is that the instrument has tremendous versatility.

“The accordion is such a staple instrument to so many different types of music,” he added. “It’s in so many types of music we hear on a daily basis.”

The accordion has lost much of the stigma once attached to it, Theriault said, especially among younger people.

“People have traveled more, and recognize different types of music,” he said. “Younger generations are using alternative instruments in their music. People hear something different, and the natural reaction is to pick up on it, and give it respect and attention. It’s the right time to play an instrument that’s above the ordinary.”

Actually, accordion was Theriault’s first instrument. His father, Joe, a merchant sailor during World War II, took his accordion around the globe, and came home playing all kinds of world music. The younger Theriault learned to play by ear starting around age 5.

It was only rock ‘n’ roll, but Theriault liked it, so by age 12 or 13, he was shedding the accordion for something that could be amplified, learning synthesizer and other keyboard instruments so that he could rock.

For the next quarter century, Theriault was a working musician, playing standards, Top 40, jazz and oldies from the ’50s and ’60s, both in sessions and live, across the country.

“There were few musicians around [during much of his career], and there was incredible demand,” he said. “I was never out of work, and made good money.”

In the early ’80s, the music industry was changing, with tougher drunken-driving laws going on the books and an influx of aspiring musicians. Also, Theriault needed something new.

“I spent so much time in an atmosphere I wasn’t involved in, because I didn’t drink or smoke,” he said. “I needed a cleaner environment.”

One of his then-band mates was a watchmaker, and he introduced Theriault to the jewelry business. He was attracted to gemology because it was esoteric and specialized. As a result, he studied to become a gemologist and has had his own business for 16 years, gradually phasing out music.

Still he missed performing. And, once again, his father had the answer.

At age 80, Joe Theriault, who picked up the accordion again five years ago, is the Port City Busker, playing on the streets of Portland during the summer. He encouraged his son to try the instrument again as well.

“I needed to find something to play that wouldn’t involved a tremendous amount of setup time and equipment,” the younger Theriault said. “The accordion is a keyboard that’s portable, and not a lot of people are playing it. Guitarists-vocalists are everywhere. People are curious about the accordion.”

Theriault, who just started playing publicly again this past fall, uses three different accordions in his act, along with an amplifier and microphone as needed.

The first is a 1957 Excelsior, made in the United States.

“It’s the most mellow-sounding, a good jazz instrument,” Theriault said. “I try to develop a style like a jazz guitarist, with pretty complex arrangements and big fat chords. It’s great for Spanish and Brazilian music.”

Next is his “flea-market find,” a vintage ’50s Italian Supra with a mother-of-pearl body and blue keys, which he picked up for $60.

“It’s got a certain tuning that’s fantastic for Parisian cafe music,” he explained. “I also use it for Cajun and zydeco when it’s amplified. I get more versatility out of this one.”

This summer, he picked up a Hohner button box, an instrument more akin to a harmonica.

“It’s a happy instrument,” he said. “People are always smiling when they hear it. It gets people’s feet a-tappin’.”

Theriault, who plays several nights a month at clubs, pubs and private parties, admits that accordion isn’t his favorite instrument. It’s a means to an end.

“It’s a vehicle,” he said. “I love music so much and I love to perform for people. It just gets me in the game again.”

For information on the Custom House show, call 596-7447. For more information on Theriault, call 236-3933.