While other studies have shown that people commit fewer crimes when they get married, this is the first to show that people straighten up their act even before they tie the knot, researchers said.
"You may start to act married even before the wedding," said Rachel Arocho from Ohio State University in the US.
"This is a reminder that marriage still matters. "Just the expectation of marriage may be enough to change some people's behaviour," said Claire Kamp Dush from Ohio State.
The participants were asked in 2000 and 2001 to estimate the per cent chance that they would be married in five years.
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They were also asked whether they had committed certain delinquent acts - including property theft, personal assault, drug dealing and property destruction - since the last time they were interviewed for the study.
On average, participants in 2000 thought there was a 43 per cent chance they would be married within five years, increasing to 48 per cent in 2001, researchers said.
In 2001, participants reported slightly fewer delinquent acts, with 1,273 reporting an average of 1.62 incidents of misconduct.
The key finding was that young people with higher marital expectations in 2000 had lower levels of delinquent activity in 2001, researchers said.
Delinquent activity did not seem to be strongly associated with later marital expectations, they said.
"It seems that young people think of marital expectations independently of their current participation in delinquency or crime," said Kamp Dus.
They probably feel they have to watch their behaviour to gain social acceptance and be seen as "marriage material," she said.
"Plus, people with a job, good income and education all have a better opportunity to get married - and delinquency stands in the way of achieving these goals," said Arocho.
The findings were published in the Journal of Marriage and Family.