The shooting happened on Tuesday at the Centre for Advanced Medicine and Neurology of Nevada in Renown Regional Medical Centre.
Reno deputy police chief Tom Robison said: "We have two people confirmed deceased in the building, two others injured."
The regional medical centre is the largest hospital in northern Nevada. It was locked down amid the chaos.
Police rushed to the scene and victims were treated by doctors at the hospital.
More than 30 police cars, including SWAT team vehicles, surrounded the sprawling medical complex and closed off a three-block area near central Reno.
State senator Debbie Smith said she was at Renown for an appointment and was trying to leave a nearby building when the shooting started.
She added: "I encountered some SWAT team guys, they said nobody was leaving.
"A police officer was at the door and said I couldn't go out there."