By early April, 30 trespass notices had been issued by the university proctor's office this year, about 70% involving tertiary colleges of residence.
It is understood that in at least some cases, the second-year students, now living in flats elsewhere in the city, had decided to make their impromptu return visits after having a few drinks with friends.
Student Services director David Richardson said that problems with returning students were "not a new issue" and the numbers involved were similar to previous years.
Many of the trespass notices had been issued to "curious second-year students returning to their former college of residence to see who is now in `their room'.
"While the visits are essentially curious, harmless and sometimes annoying, they do introduce potential security issues," Mr Richardson said in a written reply to questions from the Otago Daily Times.
There was a "nuisance aspect for both college management and new college residents".
"The colleges are `home' to students for the duration of their stay.
"It's great that people feel such a strong connection to their college, but they need to respect that it's now someone else's room and home for the year," Mr Richardson said.
"The new residents have a right to privacy - just like anyone else would in their home."
Jan Burton, deputy warden at St Margaret's College, said that night-time nostalgic visitors were a rarity at the college.
Welfare staff were on duty at night and systems were in place to prevent unauthorised visitors, including former residents, from wandering about the college complex, Ms Burton said in an interview.
Former residents with "warm feelings" often made sentimental journeys back to their former home college by day, as well as parents who had returned to Dunedin to attend their children's graduation ceremonies.
Such visitors were given guided tours around the complex and the college had also developed an active alumni network to keep former residents in touch, she said.
