Cameron made the case for the United Kingdom in an article published in The Scotsman. He was scheduled to travel to Edinburgh to make his case in a speech and to pay what his office described as a "courtesy call" on Scottish First Minister Alex Salmond.
Salmond has said he hopes to discuss terms of a referendum on Scottish independence directly with Cameron. The British government says talks should be with the minister for Scotland.
The first minister put his own spin on the visit.
"Courtesy visits are usually what prime ministers do to foreign heads of state -- I don't know if that's what Downing Street meant to imply," Salmond said this week.
In his Scotsman piece, Cameron said he was arguing as prime minister of all Britain and not as head of the Conservative Party.
"Of course, there are arguments that can be made about the volatility of dependence on oil, or the problems of debt and a big banking system. But that's not the point. The best case for the United Kingdom is entirely positive," Cameron said. "We are better off together. Why? Well, first of all, let's be practical. Inside the United Kingdom, Scotland -- just as much as England, Wales, and Northern Ireland -- is safer, richer and fairer."
The trip is Cameron's first to Scotland since Salmond put forward plans for a referendum in 2014.