Abstract. The HIV-related Attitudes Scale (HIV-AS) is a brief, valid, and reliable instrument, widely used in Spain. Because of the high risk of HIV in adolescents in Portugal and the scarcity of multidimensional measures to assess attitudes toward HIV-related aspects, reliable and valid instruments are essential for understanding sexual risk behaviors in this population. The aim of this study was to adapt and validate the Spanish version of the HIV-AS into Portuguese. Factor structure, internal consistency, temporal stability, and measurement equivalence with the Spanish version were examined. Analyses were conducted based on a sample of 1,618 adolescents aged 15–18 years (Portugal N = 624, and Spain N = 994). This study confirmed the four-factor structure of HIV-AS, including attitudes toward obstacles to safe sex, HIV testing, condom use, and people living with HIV/AIDS. Reliability was excellent (α = .82) and temporal stability was moderate ( r = .51). Results provided good initial support for the invariance at a strict level for Portuguese and Spanish samples. The Portuguese version of the HIV-AS is a valid and reliable tool for assessing relevant dimensions of attitudes toward HIV-related aspects in adolescents. Future research is needed to consolidate these findings and to generalize them to other populations and countries.