Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of clothing retailer Aeropostale (NYSE: ARO) were looking very unstylish to investors today as they fell as much as 20% after the company's first-quarter earnings report.

So what: Earnings per share fell 58% from last year to $0.40, while revenue inched up 1% to $469 million. Sales were slightly softer than expected, but Wall Street was well-prepared for the drop in earnings and had predicted $0.40 per share. However, they weren't as prepared for the company's second-quarter guidance. Management sees earnings per share in a range of $0.11 to $0.16 for the upcoming quarter, which is easily short of the $0.27 that Wall Street was hoping for. Inventory and rising costs appear to have a big hand in the lackluster expectations.

Now what: Aeropostale CEO Thomas Johnson said the company is "disappointed with our current performance," and I'm sure investors feel the same way -- though possibly with less-publishable words. On the upside, the company does still sport an impressive debt-free balance sheet with roughly $140 million in cash, and it's aggressively buying back its own shares. But with margins plunging from a year ago and the operating environment not improving quickly, the company needs to get its act together or investors will continue to find other places for their money.

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The Motley Fool owns shares of Aeropostale. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.

Fool contributor Matt Koppenheffer does not have a financial interest in any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or Facebook. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.