Hamm has at least one large polyp on his vocal cords and will undergo a procedure in Boston to have it removed. He discovered the polyps after coughing up blood.
"He's having a single polyp removed from his throat," his representative said, and it should be a "routine outpatient procedure."
Fellow "Mad Men" actress January Jones was reportedly talking about the story at an Emmys afterparty Sunday night.
Hamm, 42, was nominated for the Outstanding Lead Actor in a Drama for the AMC series. While he did not win, he did take the stage for another award, when he revealed his unusually raspy voice.