This study intends to assess the predictive power of the variables of perceived social support from friends, friendship quality and attachment to friends, concerning the loneliness level of adolescents. The research sample undertaken via the descriptive method comprises of 430 students, 239 female and 191 male, at the Anatolian high schools of the İskenderun district in Hatay province in the 2016-2017 academic year. The study data was obtained by using the Personal Information Form, UCLA Loneliness Scale, Perceived Social Support Scale, Friendship Quality Scale and Adolescent Friendship Scale. While research variables were examined in terms of gender, educational level of the parents, number of siblings, family income level and class level, the T-test, ANOVA, Kruskal Wallis H test were used for the SPSS package program. A hierarchical multiple regression analysis was used to determine the degree to which the variables of perceived social support, friendship quality and attachment to friends predict loneliness. The study concludes that the perceived social support from friends, friendship quality and attachment to friends variables significantly predict loneliness. It was observed that loneliness, one of the research variables, did not differ according to gender, grade level, educational level of parents, number of siblings, or monthly income level of the family. On the other hand, it was seen that friendship quality and perceived social support differed significantly in terms of gender, and female students received more social support than male students. It was also seen that these variables did not differ significantly according to class level, educational level of parents, number of siblings, and monthly family income level. Finally, it was observed that the secure attachment subscale of the adolescent friendship attachment scale showed significant variations in favor of female students. All these results were discussed in the light of other studies in the literature within the context of adolescence, loneliness, social support, attachment and friendship quality variables.