The whiskered animals are becoming more commonplace as "more people eat out, take fast food and go to the growing numbers of food trucks and stands," according to Sven Jeppsson, spokesperson for Swedish pest control firm Anticimex.
He also notes that household waste is increasingly being stored outside apartment blocks, rather than indoors.
"So the rats have more opportunities to source food from us and multiply than when we just dined at home," he tells The Local.
Across Sweden, 33,960 cases of rats were reported in 2013, compared to 29,006 in 2011.
Figures for 2014 are expected to show "another big rise around the country," when they are released in January, says Jeppsson.
"We can't tell you the figures yet, but numbers are most definitely going up," he added.
Stockholm is the worst affected city in Sweden, with older buildings in Södermalm and Gamla Stan (the Old Town) most susceptible to infestations.
"They may not have the same waste facilities as other buildings or it can be the case that when they are renovated, rats come up through the drains," says Jeppsson.
He adds that rats have "fewer places to go" in newer apartment blocks in the suburbs.
His advice to people worried about rats is to ensure that toilet pipes remain sealed at all times, even during building work.
Traps and poison can be used to target the rodents before professional pest controllers are called in.
Earlier this year a Stockholm family made global headlines when they found an animal measuring 40 centimetres (not including the tail) in their kitchen in Solna in the north of the city.