Costco Wholesale Corp. (COST), the largest U.S. warehouse club, posted quarterly earnings and sales just below estimates Wednesday, sending its stock 3.3 percent lower.

Profit for the second fiscal quarter ended Feb. 13 rose to $305.5 million, or 62 cents a share, from $226.8 million, or 48 cents a share a year earlier, the company said in a statement.

Excluding the impact of a $52.1 million income tax benefit and a $16 million cumulative charge to preopening expenses, Costco said net income wo have been $263.3 million, or 54 cents per share, for the fiscal second quarter.

Analysts, on average, expected the company to earn 55 cents per share, according to Reuters Estimates.

"People are a little bit concerned about the margins. Costco has talked about taking operating margin from 2.8 to 4 over a six-year period, so that equates to about 20 basis points of operating margin expansion. And in this quarter they did 13," said Mitchell Kaiser, analyst at Piper Jaffray.

Costco said second-quarter sales increased to $12.41 billion from $11.33 billion. On average, analysts were expecting sales of $12.58 billion. Sales at stores open at least a year, a key measure for a retailer, rose 7 percent.

Costco shares fell $1.56 to $45.15 on Nasdaq.

Costco released its results a day after rival BJ's Wholesale Club Inc. (BJ) posted a 10.2 percent rise in its quarterly profit excluding a charge from lease accounting. BJ's, whose shares rose more than 8 percent Tuesday and were up 2.7 percent on Wednesday, said the strength of its private label brand boosted its operating margin and spurred profit growth.

While Costco was affected, like many others, by some accounting changes, its selling, general and administrative expenses were also disappointing, another analyst said.

"It was a little bit below expectations from a sales and earnings standpoint. If you look at the trends within the numbers, gross margin was up 9 basis points and looked to be a very good numbers. What investors will probably find disappointing on the margin will be the minimal amount of SG&A leverage that they saw in the quarter, down 2 basis points," said Jeff Stinson, analyst at FTN Midwest Securities Corp.

Stinson also noted that CostCo's February comparable store sales, though overall in line with expectations, were "a little disappointing" in the United States.

Costco, which competes with Wal-Mart's (WMT) Sams Club (search) as well as BJ's Wholesale, said February comparable store sales rose 7 percent.

Costco, based in Issaquah, Washington, operates 451 warehouses in the United States, Puerto Rico, Canada, Britain, Korea, Taiwan, Japan and Mexico.