Sales dropped to a seasonally adjusted annual rate of 4.62 million, the lowest level in two and a half years, the trade group said.
"Disruptive and prolonged winter weather patterns across the country are impacting a wide range of economic activity, and housing is no exception," said NAR Chief Economist Lawrence Yun.
"Some housing activity will be delayed until spring. At the same time, we can't ignore the ongoing headwinds of tight credit, limited inventory, higher prices and higher mortgage interest rates," he said.
NAR said the median home price for an existing structure in January was $188,900, a 10.7 percent rise from the same month a year earlier.
Sales of distressed homes accounted for 15 percent of all sales, up 1 percentage point from December, but down from the 24 percent level in January 2013.
Out all all sales, 11 percent involved homes in foreclosure.
At the end of the month, the national inventory, 7.3 percent above a year ago, represented 4.6 months of inventory at the current rate of sales -- making it a sellers' market, short on supply. It takes a 6-to-6.5-month inventory to create a balance between buyers and sellers, NAR said.