Standard & Poor's also assigned its AAA rating to the city's 2013 GO bonds. The outlook is stable.
"The ratings reflect the city's strong and conservative management practices that, when combined with a focus on predictability and stability, has led to a trend of very strong financial results," said Standard & Poor's credit analyst Hilary Sutton.
The AAA ratings reflect the city's: location and participation in large regional employment centers; very diverse property tax base with low unemployment, extremely strong per capita market value, and strong-to-very strong incomes; very strong financial position, with strong management practices and policies; and low-to-moderate debt burden.
The city's unlimited property tax pledge secures the bonds. Officials will use bond proceeds to finance a variety of capital improvements and refund certain outstanding bonds.
Portsmouth, with a population of about 21,000, is located along New Hampshire's coast, approximately 50 miles south of Portland, Maine and 50 miles north of Boston.