NEW YORK — Jim Chanos, founder of Kynikos Associates, revealed Thursday a stock he has been shorting for years: kidney dialysis company DaVita.

"It's always interesting in my world when one of your biggest customers is suing you for fraud," Chanos said at the Delivering Alpha conference presented by CNBC and Institutional Investor, referring to a lawsuit from health insurer Blue Cross of Florida.

"Most dialysis patients are old and less affluent and qualify for Medicare and Medicaid in the vast majority of cases," Chanos said. "What DaVita is trying do is push those patients into, ironically, more expensive insurance contracts through the Obamacare exchanges."

"They then turn around and charge the commercial payer three to four times what they get from Medicare and Medicaid," Chanos said, referring to the lawsuit.

He added that while the American Kidney Foundation can agree to pay some of the higher commercial costs, DaVita is one of the two largest donors to the foundation. "So, they are donating to the charity; the charity is then paying the premium into the Obamacare exchange; then they're charging the insurers 3x-to-4x."

DaVita shares fell to their session lows following Chanos' comments, and were later down 3.2%. The stock had risen more than 17% this year but is down more than 13% over the past year.

Chanos, whose firm manages around $2 billion in assets, said in 2017 he was betting against dialysis companies. Thursday market the first time he revealed DaVita as one of his short positions.