Irrational beliefs (IB) are irrational thinking patterns that limit the interpretation of situations and generate difficulties in daily life. Although there are several instruments to evaluate irrational beliefs, attention to their evaluation in adolescents has been insufficient, and possible gender and cultural differences have been overlooked. This study aims to analyze the psychometric properties of the Irrational Beliefs Scale-Adolescent Form (IBS-AF) in adolescents from Peru and Turkey aged 13 to 18 years (M = 15.1, SD = 1.17), where 52.7% were females. Two models were evaluated using confirmatory factor analysis, where the second unidimensional model of 15 items with adequate fit indices (X[superscript 2]/df = 4.79, CFI = 0.959, TLI = 0.952, SRMR = 0.065, RMSEA [95% CI] = 0.078 [0.72, 0.84]) and adequate reliability was confirmed. Factorial invariance (configural, metric, scalar, residual) was also evaluated based on country and gender, as well as differences between these categorical variables. In conclusion, IBS-AF is a consistent and reliable tool for evaluating irrational beliefs in adolescents and is equivalent in both cultural contexts and based on gender. Furthermore, significant differences favor women and Turkish adolescents in IB scores. This scale will be useful in addressing IB in adolescents and improving their psychological well-being.