Oliver was the most popular boy's name in NSW for the second year running, given to 607 babies in 2015, NSW Registry of Births, Deaths and Marriages reported.

Charlotte ascended to the number one spot for girl's names, bestowed on 529 newborns in 2015.

While scores of parents chose Charlotte after the Duke and Duchess of Cambridge did the same, the Thorsteinssons were not thinking of anyone famous when they made their selection.

"We didn't pick Oliver for a special reason," Mr Thorsteinsson said.

"We just liked the sound of it."

The first-time father said they chose the name early and came back to it later after their new bundle of joy was born at Dubbo Hospital in September.

"It sounded right when the midwife asked us what we were going to call him," Mr Thorsteinsson said.

"We both said Oliver at the same time - so it was lucky."

William, Jack, Noah and Lucas rounded out the top five boy's names in 2015.

Charlotte overtook last year's most popular, Olivia, which fell to number two, with Mia, Amelia and Chloe also featuring in the top five.

NSW Registry of Births, Deaths and Marriages registrar Amanda Ianna says names "will come in and out of vogue with special events, famous people, and political change".

"Charlotte spiked in popularity following the birth of Princess Charlotte last year and we expect that trend to continue with 2016 being the 200th anniversary of Charlotte Bronte's birth."

Ms Ianna said NSW parents were favouring traditional names such as William and Jack that were popular a century ago. Social researcher Mark McCrindle said parents were opting for "the traditional over the trendy".

"Parents are looking for something solid and significant," he said.

"They know the name they're choosing becomes their email address and their website and their Twitter handle.

"They do need a name that's easy to spell, that's not too creative, that you don't have to explain all the time."