Our friends at the Securities and Exchange Commission closed their last fiscal year in September and have tallied all of the investor complaints they received during that period. Topping the list of complaints, as in previous years, were brokerages.

According to a Reuters report, "... about 31% of all complaints lodged with the SEC concerned brokerages. There were fewer complaints about corporations, mutual fund companies, investment advisors, and transfer agents." The brokerage complaints can be divided into five categories, in order of number of complaints: transfer-of-account problems (with 622 complaints); unauthorized transactions; account-closing complaints, including problems with redemptions or liquidations; account records, specifically customer statement errors or omissions; and unsuitable recommendations.

This information tells us a few things. For starters, it's good to be careful when you pick your brokerage. You might, for example, ask questions and get opinions and recommendations on our Discount Brokers discussion board. The website of the National Association of Securities Dealers can also advise you on how to protect yourself as an investor.

The complaints also reveal some investor naivete. Many complaints about unauthorized transactions, for example, were from people who didn't understand that as they'd invested on margin, their brokerages had the right to sell off some stocks in the event of a margin call.

Another frequent problem is that investors can't always make sense of their brokerage statements. In some cases, the brokerages could (and should) be clearer -- while in others, investors simply need to learn more.

Note that some brokerages find it useful to withhold some information that investors might like to see, such as how much various investments have fallen in value over certain time periods.

The bottom line is that the more you know about the stock market and how brokerages and brokers work, the better off you'll likely be. For an eye-opening start, check out this article by Nathan Slaughter, on why he failed as a broker.

Spend a few minutes in our Broker Center, and you may find a brokerage that will serve your needs better and cost you less than your current brokerage. Indeed, some very reputable brokerages now charge commissions of $5 or less per trade. (Our comparison table may be particularly helpful.)

You might also want to poke through the websites of some major full-service and discount contenders for your investing business. Examples of full-service brokerages include Merrill Lynch (NYSE:MER), Citigroup's (NYSE:C) Smith Barney, and Morgan Stanley (NYSE:MS). Examples of discount brokerages include Fidelity, Ameritrade (NASDAQ:AMTD), E*Trade (NYSE:ET), and Charles Schwab (NASDAQ:SCHW) -- which is a Motley Fool Stock Advisor recommendation.

Longtime Fool contributor Selena Maranjian does not own shares of any companies mentioned in this article.