What do you get when you combine a clear and compelling retail strategy with superior execution and a growing and lucrative market segment? The answer is a comparable sales growth machine. Call it Walgreen (NYSE:WAG) for short.

The company just reported sales results for March, and the numbers are nothing short of what we have come to expect. Total sales grew 12.8% for the month, with sales growth at comparable stores notching an 8% gain. This follows comp store increases of 8.9% in the second quarter, which follows 9.7% in the first quarter, which follows an average of 8.9% for each of the past three fiscal years. You get the picture.

The blend of comps was 8.8% in the pharmacy (made up of 4.4% more prescriptions filled) and 6.5% in the front end (all the other stuff in the store you pick up while waiting for your presciption to be filled).

The calendar was moderately unkind to Walgreen during March. The month had one more Saturday and one fewer Wednesday than last year, cutting into pharmacy sales growth by 1.4%. Customers fill more prescriptions on weekdays than weekends.

There was a lot of noise surrounding drugstore stocks last fall, when Wal-Mart (NYSE:WMT) announced $4 per month pricing on 300 prescription drugs, and Target (NYSE:TGT) quickly followed suit. The fear was that this aggressive pricing move by the big-box discounters would siphon off customers from the drugstore segment.

This doesn't seem to be the case; in fact, there appears to be a slight but perceptible uptick in comp sales growth at both Walgreen and CVS (NYSE:CVS) over the past two quarters. Both companies continue to run high single-digit comps. Sales growth at Rite Aid (NYSE:RAD) also appears to be unaffected, although in recent years the company has delivered much lower comp sales growth, in the low single digits.

The new-store side of growth at Walgreen is also proceeding at a machine-like pace. The company remains on track to add a net increase of 400 new stores this year, on its way to 7,000 stores by the year 2010. The forward-looking real estate strategy at Walgreen perhaps doesn't get as much attention as it should. Eighty percent of the current store base has been built in the past decade, with only 8% of the stores open in 1990 still operating in their same location. The company continues to invest heavily in renewing its store base, and ensuring that its stores occupy the best locations.

Is there any end in sight for this growth machine? I wouldn't count on it in the near term. The stock trades at a P/E of 24 times trailing-12-month earnings, about one-third higher than the average of all S&P 500 companies. You get what you pay for, and superior companies on the top of their game don't (usually) come cheap.

For more news on the drugstore growth saga, check out:

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Fool contributor Timothy M. Otte surveys the retail scene from Dallas. He owns shares of Wal-Mart, but none of the other companies mentioned in this article, and welcomes comments on his articles. The Fool has a disclosure policy