BusinessWeek tracked down 18 high-powered women to discover why they traded the relative security of a big company for a startup, and to find out what their experiences can teach other entrepreneurs. Working with executive recruiters, women's business groups, venture capitalists, angel investors, and other successful entrepreneurs, we identified women who had left senior positions at large companies, where they typically had profit-and-loss responsibility for multimillion-dollar units, to start their own companies. Also included were a handful of women who took the helm of existing small companies in order to transform them.

Nancy Anderson, 59, ran a $1 billion business in Hewlett-Packard's computer systems division. But in 1990, when her son was two years old, Anderson decided her traveling days were over. She held a series of part-time management positions over the next decade, including interim CEO at a technology company. In 2005, she became CEO-and the eighth employee-of Palo Alto (Calif.)-based Blue Vector Systems, a technology company focused on radio frequency identification systems. At HP, she says, she always wondered if the business would have gone on just fine without her. "But in a small company, it is more clear you make a difference," Anderson says. "And that's more fun."