The tragedy happened in Afragola, a city in the province of Naples, Italian local daily Il Mattino reported.
According to the paper, the mother, aged 59, hit her disabled son several times on the head with a hammer. She then lay him down on the bed before stabbing him in the throat with a kitchen knife. The woman then attempted to take her own life with the same knife and is now in hospital in a critical condition.
Her 23-year-old son, identified only as M.G. by La Repubblica, had been disabled since birth.
The two were discovered around 2.00pm by the woman’s daughter when she returned from work.
Last month, a woman in northern Italy killed her three children, reportedly telling police afterwards that she was "desperate" and in poverty after her husband left the family.
Also in March, a woman from the southern Italian region of Calabria allegedly stabbed her 11-year-old son to death over her husband's affair.