Any people who are related either as parent and child, grandparent and grandchild or as brother and sister (including half-siblings) who have sexual intercourse with each other are guilty of an offence. This does not include a family member related by marriage or adoption alone.
Maximum penalty: 10 years imprisonment
[Criminal Law Consolidation Act 1935 (SA), s 72]
The consent of the parties to the sexual intercourse is irrelevant, however, ignorance of the relationship may be a defence (for example, a brother and sister separated from birth and unaware that they are related) [s 72(2)].