The purpose of this study was to examine the factors associated with adolescents' attitudes towards peers identified as having special educational needs (SEN) in Portuguese mainstream schools. A sample of 813 students (5th to 9th grades) participated in this study. Data were collected using the Chedoke-McMaster Attitudes towards Children with Special Needs Scale, the KIDSCREEN 10 Quality of Life Scale, and the Social Support Appraisal Scale as well as a brief sociodemographic questionnaire. The results indicate that perceiving social support from family and teachers and having a friend or a family member with SEN is associated with more positive affective and behavioural attitudes towards peers with designated SEN. Perceiving social support from the family and having a classmate or a family member with SEN was associated with more positive cognitive attitudes. After the remaining variables were controlled, the perceived quality of life was not uniquely related to attitudes towards SEN. The importance of these findings for research and practice is discussed.