John Hancock Preferred Income Fund III is a closed-end, diversified management investment company. The fund's primary investment objective is to provide a high level of current income, consistent with preservation of capital. The fund's secondary investment objective is to provide growth of capital to the extent consistent with its primary investment objective. The fund seeks to achieve its objectives by investing in securities that may be undervalued relative to similar securities in the marketplace. The portfolio composition of the company consists of U.S. preferred securities, foreign preferred securities, common stocks, corporate bonds, and short-term investments.