Rates of reported sexual assaults and rape increased sharply after 1980. The increases were partly a consequence of changes to legislation relating to sexual violence, particularly the 1985 amendment to the Crimes Act 1961, which introduced the category of 'sexual violation' and made rape within marriage a crime. It also became somewhat easier to report sexual assault after 1980. Reports of sexual assault from this time onwards also included an increasing number of historical sexual offences. The increases were particularly high in the late 1980s, early 1990s and early 2010s.

Note: 'Sexual assaults' is a category of amalgamated offences used by the New Zealand Police to report crime statistics. It includes acts, or intent of acts, of a sexual nature against another person, which are non-consensual or where consent is proscribed. 'Rape' is part of this broader sexual assaults category and is made up of the offences: 'Males rapes female under 12', 'Males rape female 12-16', 'Males rapes female over 16', 'Husband rapes wife', and 'Male rapes women (no weapon)'.