As with any investment, there’s the chance that you will lose money with an ETF. If the ETF drops in value, you could lose some of your principal.
Risk specific to ETFs is something called contango. This risk is especially pronounced with ETFs that rely on futures contracts, like commodity ETFs. If expiring contracts are less expensive than front-month contracts, the value of an ETF can drop steeply as the contracts rollover. When investing in ETFs that involve futures, be careful of this situation.