Louis travels to a hospital in San Francisco to meet transgender children and their families, as they undergo life changing treatment.
In this fascinating documentary, Louis meets children embarking on an unusual journey.
We'll bet you don't know everything about our favourite film-maker...
Louis Theroux traces the fortunes of different people suffering from alcoholism.
Louis Theroux meets people living with the long-term effects of a brain injury.
Louis visits Coalinga Mental Hospital, which houses more than 500 convicted paedophiles.