Former professional basketball player Kwame Brown is crying foul on Merrill Lynch, saying the brokerage stole $17.4 million of his investments.

Brown said in a lawsuit that his signature was forged on various authorization forms and agreements, allowing his financial adviser to make investments and stock trades without his consent.

When Brown sought an accounting of his investments last year, he was told he had no monies with Merrill Lynch, according to his complaint filed Thursday in Los Angeles.

Brown,...