Brandon Maso says he's a responsible teenager. But that wouldn't be enough to keep him out of trouble if he's caught outdoors after midnight in Frisco.

Beginning tonight, the city is imposing a curfew that orders children under 17 indoors between midnight and 6 a.m. daily. A violation can mean a fine of up to $500.

For years, Frisco had no curfew, even as nearby cities imposed one, including Plano, McKinney and Allen.

But Mayor Mike Simpson said that because of rapid growth in the city and school district, it was better to be safe than sorry.

"We figured we were taking a proactive step so that our kids wouldn't be put in the position of getting into trouble," he said. "And if Frisco was the only one who didn't have it, you might have teens saying, 'Hey, let's go to Frisco, they don't have a curfew.' "

Since 2000, the population of Frisco has nearly tripled, increasing to more than 92,000 residents this year. The city hasn't seen a major increase in juvenile crime, Mr. Simpson said, but instead wants to reduce the chances of youths being victims of crime, among other goals.

Juvenile crime has gone both up and down in Frisco in recent years, according to statistics recently presented to city leaders by police Chief Todd Renshaw. For example, criminal mischief has gone up overall but leveled off during curfew hours. Meanwhile, car burglaries have gone up and down in recent years but climbed during nighttime hours.

The City Council approved the curfew in a 4-2 vote in August. Council members Tony Felker and David Prince opposed it, saying there was no proven increase in crime and that parents, not the city, should oversee their children.

Brandon, a junior at Centennial High School in Frisco, said he also opposes the curfew.

"You're finding someone guilty of something before they've done anything wrong," said Brandon, who unsuccessfully lobbied the council in August to vote against the curfew. "If you catch me smashing a car window and stealing something, then arrest me. But just because I'm out after midnight?"

Mr. Prince, who said he agreed with many of Brandon's arguments, said he stands by the council's decision and trusts the Frisco police.

"They're not going to be using this law to make our teenagers' lives miserable," he said. "They'll be using it to provide assistance and make sure our kids get home on time."

Exceptions to the curfew are allowed if the juvenile is with his parents; on a parental errand without detour or stop; working or traveling to work; involved in an emergency; or attending an official school, religious or recreational activity.