The study aimed to examine the psychometric properties of the Dutch Life Orientation Test-Revised for Adolescents (LOT-R-A), a self-report questionnaire assessing dispositional optimism, and to evaluate the two-factor structure (optimism, pessimism). The LOT-R-A and the questionnaires measuring well-being (MHC-SF-A) and psychological problems (SDQ) were completed by 459 Dutch adolescents (178 boys and 281 girls) between the ages of 11 and 18 years at baseline and 281 adolescents at a four-week follow-up. The results confirmed the two-factor structure (optimism, pessimism) of the LOT-R-A. The findings provided evidence of internal consistency of scores ranging from low to good, and evidence of good test-retest reliability of scores. Further, scores of optimism were cross-sectionally positively associated with scores of positive emotions and well-being and negatively with scores of psychological problems and negative emotions, providing evidence of convergent and divergent validity of optimism scores with emotions, well-being, and psychological problems. Lastly, scores of optimism were prospectively positively associated with scores of well-being and negatively with scores of psychological problems, providing evidence of criterion validity of optimism scores with well-being and psychological problems. Based on these findings it can be concluded that the LOT-R-A is a valid instrument to examine optimism among adolescents. Future research can help to elucidate the role of optimism in mental health interventions and can gather knowledge on how these interventions can be refined to optimally cultivate optimism during the developmental period of adolescence.