Mating rivalry is not only limited to one's ingroup, but also outgroup members can be perceived as potential romantic competitors. In the present research, intergroup intrasexual competition (IIC) is defined as the extent to which individuals react negatively towards potential outgroup same-sex members in the context of mating competition. The authors present a scale developed to assess individual variation in IIC. The scale was administered to five student samples: 78 Dutch, 396 Dutch, 105 German, 306 Latvian and 96 Russian. Through a factor analysis, a long version of the scale was reduced to a 12-item version. A moderate test-retest correlation was established. IIC correlated positively with intrasexual competition, social dominance orientation, possessive jealousy and perceived vulnerability to disease, serving as indicators of convergent validity. As predicted, men scored overall higher than women on the IIC scale, but not in the samples where the participants came from a national minority group (Germans in the Netherlands and Russians in Latvia). Latvian male participants showed the highest level of IIC, followed by the Russians, the Dutch and the Germans.