Objectives: To assess brain oscillations in very preterm and full-term born adolescents and explore subgroups based on integrative patterns of brain oscillations with different frequencies. Additionally, subgroups were related to functional outcomes and very preterm birth. Methods: A Dutch cohort of 53 very preterm and 61 full-term born adolescents aged 13 years participated. Resting-state electroencephalography was recorded. Absolute and relative delta, theta, alpha, and beta power were compared between groups. Latent class analysis (LCA) was used to identify subgroups with distinct activity patterns and to relate these patterns to intelligence, academic performance, motor skills, and very preterm birth. Results: Very preterm adolescents exhibited decreased relative beta activity. LCA with four classes showed the best model fit. The class with the highest level of delta and lowest levels of theta, alpha, and beta power was associated with lowest intelligence, academic, and motor estimates. Very preterm born adolescents were more likely than controls to be members of this class. Conclusion: Very preterm born adolescents showed altered oscillatory activity, indicating long-lasting effects of very preterm birth on brain functioning. Distinct activity patterns were associated with both functional outcomes and very preterm birth. Significance: Specific patterns of brain oscillations may serve as biomarkers for poor functional outcome after very preterm birth.