Nine couples of two man who killed another man, were examined. They all had signs of living together just before the delict in a symbiotic manner, as seen by the couples of the folie á deux. Although after the delict there is a — sometimes strong — tendency for symbiotic living together, sometimes again in a malignant double bind. Both syndromes can be seen as a fixation in the eparation-individuation phase. An attempt is made to divide the killing t deux in four groups:

• Killing a homo sexual (two cases).
• Killing in a sado-masochistic acting out (one case).
• Killing with financial profit as superficial motive (five cases).
• Killing a man and a wife, with financial, sado-masochistic and sexual motives (one case).

This article includes a review of the folie á deux literature.