Sunderland's population is dropping at one of the fastest rates in Britain, according to new Census 2011 figures.
The city's headcount decreased by 3.2%, while Newcastle's population increased by 5.2% during the same period.
It means that Newcastle is now officially a bigger city than Sunderland.
County Durham 493,800 (+3.9%)
Northumberland 307,400 (+2.8%)
Newcastle upon Tyne 266,200 (+5.3%)
Sunderland 284,600 (-3.2%)
North Tyneside 192,000 (+4.6%)
Gateshead 191,200 (4.7%)
Stockton-on-Tees 183,800 (+4.2%)
South Tyneside 152,800 (-3.1%)
Middlesbrough 141,200 (-2.0%)
Redcar and Cleveland 139,200 (-2.9%)
Darlington 97,900 (+7.9%)
Hartlepool 90,200 (+2.0%)
Academics said that years of industrial decline was behind the fall in population, with other cities offering better job opportunities.
Professor Ray Hudson, from Durham University, explained that Sunderland had suffered because Newcastle attracted more investment.
But a Sunderland councillor argued it was about the change in housing.
Councillor Harry Trueman said: "The figures do concern us obviously. We used to be the biggest city between Leeds and Edinburgh.
"I believe one of the main factors is the demolition of nearly 4,000 of our properties with our ambitious regeneration schemes done by our housing partners. Obviously that has had a big impact on our population."
Darlington saw a 7.9% increase in its population over the 10-year period of the Census, one of the fastest increases in the region.
Academics said it was down to the enormous manufacturing base in Aycliffe, as well as strong growth in the service sector.
Overall, the North East population increased by only 2.2%: the slowest rate in the UK.