Loneliness is a pervasive social problem and is experienced universally, regardless of one's race, gender, age or cultural background. Adolescents have been reported to be the most amenable to loneliness. This study examined the influence of cultural background on adolescents' perceptions of the causes of their loneliness. In the present study, 100 Canadian youth and 206 Portuguese adolescents answered an 82-items questionnaire. The questionnaire is composed of five subscales, namely: Personal inadequacies, Developmental deficits, Unfulfilling intimate relationships, Relocation/significant separation, and Social marginality. Participants were asked to endorse those items that in their opinion constituted the antecedents of their loneliness. Results indicated significant differences, between youth of the two cultures on only two of the five subscales. Gender differences were also examined within and between cultures.