It is fairly common for Americans to change jobs — or even careers — several times in the course of a working lifetime.

When you switch workplaces, be sure to take your tax-sheltered 401(k) assets with you, but not in the form of a check that you can easily and immediately turn into cash.

Young workers in particular are inclined to make the disastrous mistake of cashing out their 401(k) accounts when they switch jobs, according to a study of 160,000 workers by Hewitt Associates, the global consulting firm.

Fifty percent of job-switching workers age 20 to 29 cashed out instead of rolling over their money to a new account. Workers were even more likely to cash out if they had $5,000 or less in their 401(k).

Even cashing out only part of your 401(k) assets when you switch jobs is a bad idea, no matter how badly you want to buy a new car, pay off student loans or erase other debts. Considering the income taxes and fees you'll pay on the withdrawal, buying a car for $20,000 would require you to remove up to $30,000 from you account. That's $30,000 that won't be accruing interest toward your retirement.

If you have the choice to roll your money into an account with your new employer, don't leave it in the account with your old employer.

You might also consider rolling your 401(k) assets into an IRA. The accounts have more investment options than an employer's 401(k) program. If you're investment-savvy, an IRA gives you the opportunity to control your money.