Walgreen (NYSE:WAG) same-store sales (SSS) rose 5.1% in June. SSS are a key measure for retailers. Total sales can grow by merely opening new stores, but SSS measures growth at existing locations. Broken down, front-end sales increased 6.8%, and pharmacy sales grew 4.2%. This is important news since front-end sales typically have higher margins than pharmaceuticals. Basically, front-end sales are everything but prescriptions, and include items such as health and beauty products.

Walgreen continues to post strong year-over-year comparisons. Last June, Walgreen's SSS rose 9%, with pharmacy sales up 11.6%. Having one fewer Thursday and one more Saturday during the month compared to a year ago, management estimated that pharmacy SSS would have been 1.7% higher. While the 2.3% SSS increase for Rite Aid (NYSE:RAD) last quarter was good, this was compared to a very weak negative 0.3% from a year earlier.

Walgreen operates in a competitive industry. Competitors include other drugstore chains like CVS (NYSE:CVS), mail-order prescription providers like Medco Health Solutions (NYSE:MHS) and Express Scripts (NASDAQ:ESRX), and mass merchants like Wal-Mart (NYSE:WMT). However, Walgreen manages to distinguish itself by expanding into prime locations and making investments in technology and customer service. Front-end sales have continued to grow by staying ahead of the curve, entering new businesses such as digital photo services.

The company continues to impress, posting positive same-store sales results month after month. At a P/E of 21, I don't find the stock rich, given the solid performance that the company delivers.

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Fool contributor Larry Rothman is happy to receive feedback, and promises to read it when not being wrestled by his three children. Feel free to email him. He doesn't have any positions in the companies mentioned.