Most likely what is happening is that you've used a non-web-safe font. (Click here for help understanding what a web-safe font is.)

The ultimate source of the font being rendered on a web page is the user’s own computer; therefore, if a user does not have a font installed on their computer, it won’t show. This means that you can use any desired font, but if the user doesn’t have it installed, the browser will default to another font – specified or not – which can lead to some seriously undesired results.

What is meant by a web-safe font is that the font is most likely to be installed on the user’s computer. This means that the font is a sure bet, being a default font included with all major operating systems such as Windows, Mac OS, and Linux. These operating systems each come with more than a handful of fonts, of course, but only a few overlap into the “universal” category. The most practical of these web-safe fonts are Arial, Courier New, Georgia, Times New Roman, and Verdana.

As for the layout of your webpage, a change in a font may cause a change in all of the design elements that surround it. If you can ensure that your font will be visible on a user's computer, your layout should be fine.

For more information about how to successfully use non-web-safe fonts, you can pick up a copy of our Web Typography Handbook. It’ll tell you everything you need to know.