Locals have told Scotland on Sunday of “big holes in huge sections” and “suspension-destroying” potholes on the 519-mile tourist trail.
Travel curbs across mainland Scotland are due to be scrapped on April 26, but residents said visitors would be shocked at the condition of the NC500 route, while was branded in 2015.
Fraser Mackenzie, a Highlands-based renewable energy project manager, said: “I’ve just driven a big chunk of what is now the NC500 - complete with numerous brand new NC500 signs - on work trips.
“It’s clearly a big marketing push, which would be great if parts of the route weren’t in such terrible condition.
"They are much worse than last year because of the weather and the cumulative effects of decades of lack of investment.”
Mr Mackenzie said the worst sections included between Bettyhill and Melvich in Sutherland, and a “suspension-destroying pothole” near Lochcarron in Wester Ross.
He said: "The surface has gone from huge sections, with an uncountable number of potholes and mere metres of newish tarmac.
"If I was driving my Ferrari around, I’d be mighty pissed off that I’d been mis-sold what is in some sections approaching a cart track.
Pete Malone, who runs Bettyhill General Merchants with his wife Susan, said: “The state of the road has got worse between here and Tongue.
"There are great big holes in huge sections.
"The council hasn’t been doing the normal maintenance, although crews have been out patching.”
Iain Gregory, of campaign group Caithness Roads Recovery, said “substantial areas” of the A99 section between Wick and John O’Groats, and the A836 west from John O’Groats, were “very bad”.
The former police area commander said: "The situation in Caithness is now so bad it is only a matter of time before a tragedy occurs as a direct result of the dangerous condition of many of our roads."
Trunk road sections of the NC500, maintained by BEAR Scotland for Transport Scotland, are believed to be better condition – the A99 and A9 between Wick and Dingwall, and the A835 between Ullapool and Braemore.
A spokesperson for NC500 Limited, which markets the route, said: “The state of our roads is a Scotland-wide issue for national/local government to address, and not just limited to the NC500.
“I don’t expect VisitScotland to be halting the promotion of Scotland as a tourist destination this summer just because some of our roads are not up to scratch.”
Highland Council, which is responsible for maintaining the non-trunk road sections that comprise most of the route, admitted the winter impact but said it would be spending an extra £20 million on road maintenance from next month.
A spokesperson said: “The recent severe weather between January and March has caused considerable damage to Highland roads.
"We have a process in place regarding potholes and defects, and all incidents that are reported are followed up.
"Our focus has been urgent road defects.
"Where resources and restrictions have permitted, we have undertaken routine maintenance works.”