A middle-aged woman who was shut into her bedroom in appalling conditions for 18 years to punish her for bearing a child out of wedlock was freed on Friday in southern Italy, police said.

The 47-year-old woman "had been held since 1990, when her family learned she was pregnant. Her son, aged 17 and a half, was found in the home," the police official said.

"We received an anonymous call telling us of the existence of a woman incarcerated in a rural home" outside Santa Maria Capua Vetere, north of Naples, police told AFP.

The woman's 80-year-old mother, older sister and younger brother were brought before a magistrate and face charges of "bad treatment and sequestration of a person," he said.

The police spokesman described "horrendous hygiene conditions" in the woman's bedroom, adding that "she showed signs of evident mental trouble, but it is unknown whether this trouble existed before her sequestration or is the result of it.