It sounds like it's more of an Excel problem than a Perl problem-- Excel doesn't seem to like large numbers, and will mindlessly convert them to scientific notation and fill the trailing digits with zeros. If you wrap your large number in quotes, it should import into excel and display properly, but will likely be treated as a string (I didn't bother to test it, but I've had it do that to me in similar cases). edit: it might also help if you prefix it with a single quote like this: '12345 which is what you do when you type entries when you want to force them to be treated as text.