Nimoy, 82, revealed on his Twitter that he suffers from COPD -- Chronic Obstructive Pulmonary Disease -- which is caused by smoking and gets worse through time.
Offering grandfatherly advice, Nimoy told his followers to "quit now!" and to "LLAP" -- his Star Trek character's famous greeting, "Live long and prosper."
The actor was spotted last month in a wheelchair at a New York hospital, attached to a breathing apparatus.
COPD is an umbrella term used to refer to a number of illnesses, including emphysema and chronic bronchitis, that are caused by smoking and damage the air sacs and passages in the lungs.
I quit smoking 30 yrs ago. Not soon enough. I have COPD. Grandpa says, quit now!! LLAP— Leonard Nimoy (@TheRealNimoy) January 30, 2014