Wal-Mart Stores Inc. will open its first in-store medical clinics under its own brand name after leasing space in dozens of stores to outside companies that operate the quick-service health stops. The world's largest retailer said it will open "The Clinic at Wal-Mart" as a joint venture with local hospital systems in Atlanta, Dallas and Little Rock, Ark., starting in April.

About 7% of Americans have tried a clinic at least once, according to an estimate by the Convenient Care Association, an industry trade group formed in 2006.

That number is expected to increase dramatically, as chains like Wal-Mart, CVS Corp. (CVS, Fortune 500), Target Corp. (TGT, Fortune 500) and Walgreen Co. (WAG, Fortune 500) partner with mini-clinic providers like RediClinic and MinuteClinic to expand operations. The trade group estimates there will be more than 1,500 by year-end, up from about 800 in November.