Drawing on data from the fifth cycle of the Program for International Student Assessment (PISA), the authors examined the relations of reported acculturation orientations--heritage as well as host culture-orientations--and perceived cultural distance between host and heritage culture with academic performance among 399 first- and second-generation immigrant adolescent students in Portugal. Results of hierarchical regression analyses, after accounting for student demographic characteristics, revealed a positive relationship between host culture-orientations and the first-generation immigrant adolescents' performance on the PISA reading, mathematics and science assessments, and also the second-generation immigrant adolescents' performance on reading assessment. Additionally, both the first- and second- generation immigrant adolescents' heritage culture-orientations were significantly negatively linked to performance on the PISA reading, mathematics, and science assessments. Furthermore, findings revealed that first-generation immigrant adolescents' perceived cultural distance was significantly negatively associated with their performance on the PISA reading and mathematics assessments. Implications for policy and practice are discussed.