Via the Irish Independent:
Yes, it's a cultural rather than a religious thing, stemming from some nasty tribal customs of South Asia and the Middle East, but though Hindus, Sikhs and the odd Christian might be perpetrators, the blunt truth is that honour killings are mainly Muslim-on-Muslim (91 per cent worldwide, 84 per cent North America, 96 per cent Europe).
Worldwide, two-thirds of victims (93 per cent women) were killed by their families of origin: 49 per cent in North America, 66 per cent in Europe and 72 per cent in Muslim countries. More than half the victims died in agony, having been either gang-raped or burned or stoned or beheaded or stabbed many times.
Being 'too Western' did for 58 per cent: this includes being insufficiently subservient, rejecting Islamic dress, wanting a career, having non-Muslim friends or boyfriends, rejecting an arranged marriage or leaving an abusive husband. This criterion covers 91 per cent of North American murders, 71 per cent of European and 43 per cent in the Muslim world. Offences against sexual propriety (eg being raped or accused of adultery) were the justification for the other murders.