By Sarah E. Needleman, reporter, The Wall Street Journal |

What’s different about building a successful for-profit and nonprofit startup?

Not much, according to Paul Graham, founder of Y Combinator, an elite accelerator program in Mountain View, Calif., that accepted a nonprofit for the first time this month, Watsi.org. “You could never tell there was a nonprofit mixed in,” he said in a phone interview on Friday.

Watsi, a medical crowdfunding platform that launched in August, is among 47 startup businesses in the latest Y Combinator class. Past graduates of the competitive three-month program include DropBox, Reddit and Airbnb.

Mr. Graham began thinking about inviting nonprofits to join Y Combinator about a year ago. “I was talking to a friend who wanted to do a nonprofit project and I realized I was giving exactly the same advice I’d be giving to a startup,” he said.