An investment account that is held joint tenants with rights of survivorship (JTWROS)* with your spouse is an excellent way of avoiding probate and an immediate income tax hit. On the death of either spouse, the account simply passes to the other without issue.
A joint investment account with someone other than your spouse can be troublesome and have potential issues that were unintended.
I have written many times about joint accounts and the problems they can cause, but here are the top 5 reasons why a joint account with rights of survivorship with anyone other than your spouse may not be such a good idea.
1. Accelerates Income Tax – Making an account joint with someone other than your spouse means you are gifting your assets and will incur a capital gain for a portion of the account. Some have suggested using a “side document” but doing so may eliminate the joint tenancy and subject the account to probate.
2. May Not Avoid Probate – Sometimes people don’t report a capital gain when making an account joint. If the other tenant is not your spouse, and you didn’t record a capital gain, then technically the account is still yours and subject to the terms of your will.
3. Risk Of Theft – Joint tenancy means the other tenants have full and unrestricted access to the assets and can take them without your consent for any reason.
4. Creditor Claims – Your joint account will subject to any claims of the other tenants creditors and will form part of their bankruptcy.
5. Divorce – If the other tenant is married and gets a divorce, the joint account is subject to the divorce assets.
Want To Find Out More About Joint Accounts?
If you want to read more about joint accounts and estate planning, take a look at The Benefits And Dangers Of Joint Accounts, The Right and Wrong Way To Split Income , Joint Ownership, Tax And Inheritance , and the Top 5 Myths About Income Tax .
This article  from Invesco Trimark is one of the best on joint accounts.
* The joint tenant ownership arrangement does not exist in Quebec and this article does not apply to residents of Quebec.