Vitamin A can be toxic in high amounts. Here's a handy guide to pre-formed Vitamin A in foods.
The Institute of Medicine recommends limiting your intake of vitamin A to no more than 10,000 IU. Note: This limit only applies to pre-formed vitamin A (retinol or retinyl), which is the type that you'll find in vitamin supplements, fortified breakfast cereals, milk, and fish.
See also: Can You Get Too Many Vitamins?
Fortunately, there's no danger of overdoing it with plant-based sources of vitamin A, which are also known as pro-vitamin A.
Here's a handy reference to the amount of preformed vitamin A in common food sources. Also, be sure to check the label of any supplements you take.
As you can see in the chart, a single serving of liver contains twice the recommended maximum. Occasionally exceeding the maximum intake is unlikely to cause a problem, but it's not something you'd want to do every day!