Fashion designer Marc Ecko had always been baffled by his passion for fashion. As a child growing up in Lakewood, N.J., he devoured comic books and videogames. So he was certain his future would include electronics and science--not fabrics and measurements. But last year at a birthday party for his 2-year-old daughter, it all became clear. As his father gazed out the window at a row of old storefronts, Ecko asked him what he was thinking about. "He said, 'That's where my grandfather's tailor shop used to be'," explains Ecko. "In that moment I realized that's why I get up some mornings with cloth on my mind."

It's all part of growing up for the former graffiti artist who, 12 years ago, at the ripe age of 20, founded his own edgy, urban-clothing line of airbrushed T shirts and baggy jeans. Targeting the influential young male so in love with skateboards, hip-hop and fluid movement, the Ecko Unlimited brand quickly amassed a fiercely loyal following. But Ecko, now married and a father of two, is gambling that these same young men want something a bit more mature--but still with flava. Marc Ecko's Cut and Sew collection, which debuts Thursday at Fashion Week in New York, features crisp linen jackets, fitted shirts and relaxed-collar suits in bright hues and creative textures like denim and gabardine. "It's really about growing up and letting the line grow up with the client," says the designer, who will still produce Ecko Unlimited for the younger crowd.

Will customers who favor baggy jeans really go for tailored slacks? Even with careful planning, altering a fashion brand's identity is tricky business. FUBU and Tommy Hilfiger have suffered drops in sales over the last few years, and some industry observers say it's partly be-cause they've lost sight of their customers' tastes. "FUBU is now making sheets. That crowd isn't looking for designer sheets to buy," says one analyst. But Ecko--whose company had sales in 2003 of more than $400 million, plus $600 million in licensing revenues--says he knows his clientele. "You have to stay out there talking to kids on the street or hanging at the mall. The moment you get away from that, you begin to get all types of ideas that have nothing to do with the guys who keep you in business."

Sure, the designer wants to expand Ecko Enterprises. But at a time when fashion is inextricably linked with entertainment (think P. Diddy and Gwen Stefani), he's focused on ventures that will excite an increasingly diverse (and aging) MTV generation. The company launched a male-lifestyle-themed magazine called Complex in 2001. More recently, it started distributing Eve's Fetish line and 50 Cent's G-Unit clothing brand. Ecko's even developing a video-game with Atari titled Getting Up: Contents Under Pressure. And the designer plans to open his first store next year in Times Square--not on Fifth Avenue. "That's not where my customers shop," he says. Spoken like a kid who knows the importance of being a grown-up.