Now I understand why the concept of "Mapril" is so popular. Depending on when the Easter holiday falls, retailers typically have a stronger-than-expected performance in either March or April, while the other month suffers. The world's biggest retailer, Wal-Mart (NYSE:WMT), did its part to help prove the theory. With Easter coming in early April this year, March sales were surprisingly strong, but the company warned of an expected drop in April comps.

For March, Wal-Mart reported a gain in same-store sales -- sales at stores open more than a year -- of 4%, more than doubling expectations. In addition to the holiday, the retailer credited its pharmacy business, where its prescription comps grew in the mid-teens. Sales of toys and lawn and garden supplies were also strong as consumers hope for warmer weather and the opportunity to get outside. Home and apparel sales were the laggards.

After the success in March, Wal-Mart expects less than ideal results in April. It estimates sales to be flat or down 2%. In the combined Mapril period, comps are expected to be up 1% to 2%. Other retailers, including Target (NYSE:TGT), announced similar results and expectations.

Although Wal-Mart is sticking by its first-quarter estimates of $0.68 to $0.71 per share, it's not exactly sounding confident. Wal-Mart's CFO said, "While the earnings guidance is still available, given the tough sales environment for the April period, it will be a challenge."

While I don't expect these latest bits of information to affect the price of Wal-Mart's stock, I do think it's still a bargain. I don't consider slow and steady growth in the U.S. a bad thing, particularly for a behemoth like Wal-Mart. I also think its strong international growth, as demonstrated by the segment's 19.3% increase in sales, should not be ignored. Add to that its decent dividend payment and discounted price, and I see the makings of a successful long-term investment.

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At the time of publication, Fool contributor Mike Cianciolo owned shares of Wal-Mart, but no other company in this article. The Fool has a disclosure policy.