Dublin city centre has been given a clean bill of health for the first time in the 18 years of a national litter survey.
The capital was graded as good as European standards but assessors warned that parts of the north inner city remain a blackspot and roads around the airport continue to be an eyesore.
Research by national trust group An Taisce for Irish Business Against Litter (Ibal) also warned that the growing number of vacant commercial properties in towns and cities is a deepening concern and tends to attract rubbish and detract from the look of main streets.
Among areas singled out for criticism are litter and dumping blackspots of Upper Buckingham Street and Marlborough Street near O'Connell Street, which the group said were in a terrible state.
Dr Tom Cavanagh, Ibal chairman, said continued pressure is also needed to clean up areas around Dublin Airport, which slipped in the survey to 37 out of 42 areas assessed.
"With Dublin City attaining litter-free status, we can say without reservation that Ireland has never been so clean. I want to acknowledge the efforts of the local authorities in bringing this about," he said.
"We have focused heavily on the roads from the airport, as these present the first impression of our country for 90% of visitors by air to Ireland and should be a showpiece for the entire country.
"But while the airport grounds themselves are spotless, the roads from it are littered. Tourism Ireland invests hugely in selling Ireland as a green, unspoilt island and the country needs to live up to this image from the moment visitors set foot here. Clearly, this isn't the case."
The survey of 42 towns and cities showed that 83% of towns and cities in Ireland are as clean as or cleaner than their European counterparts.
Nineteen were cleaner than the European average, with a further 16 in line with the average while all cities were given clean status
In their report, An Taisce inspectors said: "The worst performing sites were not just littered but subjected to long-term dumping and neglect. Upper Buckingham Street and Marlborough Place (off O'Connell Street) were both in a terrible state.
"By contrast, Shandon/Blackpool - the oldest area of Cork City - were Clean to European Norms and praised as well-presented and maintained."
An Taisce said a snapshot survey of town centres found up to one third of commercial premises are at times found lying empty with the average at about 20%.
"The issue needs to be tackled on a more systematic level, with a person in each local authority allocated responsibility for saving town centres, as has happened in Limerick, Wexford and elsewhere," Dr Cavanagh said.
"In the UK a Distressed Town Centre Taskforce has emerged to deal specifically with this issue, calling for specially designated areas where compulsory purchase orders and incentives could apply. We would welcome aggressive political initiatives here too.
"It is not just the clean environment that is at stake: these premises are part of the very lifeblood of the town. Also, visitors aren't interested in out-of-town retail parks: vibrant town centres are an essential part of our tourist product."
Overall, the report also found public parks, approach roads, and recycling areas - 62% of which were littered - had above-average levels of litter with the recycling facility at the Mayo County Council yard in Castlebar described by the inspectors as shocking.
Areas to come in for praise for cleanliness included train stations, with the Ceannt station in Galway described as gleaming.
Ibal was set up 1996 through an alliance of companies which promotes a clean, litter-free environment as a driver of economic prosperity and with An Taisce it monitors litter levels in towns with more than 6,000 people.