In an interview on Australian television, P.J. Hogan said that Mental is autobiographical, that his own father had his wife committed, hired a hitchhiker to babysit his children - he trusted her because she had a dog - and later found out that she was an escapee.
Rebecca Gibney put on 20 kilograms for the role and was in danger of becoming insulin resistant and pre-diabetic. "I was one step away from diabetes so if I had put on more weight I would get diabetes. So I stopped and we decided to employ the use of a fat suit.'' Gibney stopped her aggressive eating habits following the health scare but she didn't immediately trim down. She maintained her overweight figure for as long as she could during the shooting of the feature movie without further putting her health in jeopardy. "The double chin is all mine,'' Gibney joked.
Anthony LaPaglia was offered a part in Quentin Tarantino's Django Unchained but because Tarantino and company failed to tell LaPaglia that he got the part. LaPaglia did not know that until months later and during that time he had committed to do this movie instead.