One additional clarification, the additional paid-up insurance was purchased using the dividends received on the base policy.
What you did with the dividends is irrelevant. It's still taxable income when you cash out the policy.
Now the accuracy of that above statement assumes you had the same type of whole life policy I did. But like I said, if it's taxable/reportable on your tax return, you'll get a 1099-R (or some other tax reporting document) from the insurance company at tax time.
