Kristen LaBrie, convicted of attempted murder, wept and expressed remorse before a judge announced her punishment. She said she misses her son every day.
LaBrie's son, Jeremy, who was autistic, had a type of lymphoma with an 85 to 90 percent cure rate. He was diagnosed just after turning 7.
LaBrie, 38, thought the drugs were doing more harm than good, so she stopped the medication.
Jeremy died in 2009 at the age of 9.
Judge Richard Welch said he had sympathy for the "tremendous pressures" LaBrie faced as a single parent raising a severely disabled child.
However, Welch also said withholding the boy's treatment was "an extended, secretive and calculated act that chills the soul."
LaBrie could have gotten a maximum of 37 years in prison. Prosecutors asked for at least 16. Her lawyer sought one year in jail.
Parents who fail to seek conventional treatment for their children's illnesses have been put on notice in recent years.
Two years ago, a Central Wisconsin couple prayed instead of getting medical help for their 11-year-old daughter, who died after suffering from diabetes. They got six months in jail.
There was also the case of a 13 year old Minnesota boy who fled to California with his mother to avoid court-ordered chemotherapy. They eventually returned, and the boy received treatment. According to his doctors, he is now cancer free.
The Associated Press contributed to this report.