Event-related potentials (ERPs) were recorded during two versions of the continuous performance test (CPT) from 74 adolescents grouped into 6 yearly age intervals (12–17) in a cross-sectional study of the effects of age and sex on the cognitive ERPs. The two CPTs differed in their processing complexity, with Task B requiring an additional stage of information processing not needed for performance on Task A. The effects of Stimulus (Signal/Non-Signal), Task (A/B), and Electrode Location (FZ/CZ/PZ/OZ) were highly similar to those reported by Friedman, Vaughan, and Erlen-meyer-Kimling (1981) for a subsample (N = 30) of this group of subjects. New findings were highlighted by the analyses of the effects of age and sex on the six electrophysiological events (N150, P240, P350, P450, P550, Slow Wave) recorded during these CPTs. Principal Components Analysis (PCA) was used in an attempt to reduce overlap among components, with the factor scores compared to the baseline to peak measures. Modest age effects were found for P450 (classical P300), with the pattern of findings suggestive of differences in processing strategies between the older and younger adolescents. PCA performed on the first 408 ms of the ERP epoch yielded a component corresponding to an early-onset endogenous negativity which showed a decrease in amplitude with increments in chronological age. Effects of sex were found for P550 and Slow Wave. While the pattern of results may indicate differences between males and females in cognitive processing mode, the design of these CPTs does not allow a functional association between these components and the modes of processing that have been reported to differentiate males and females. The data highlight the importance of including age and sex as variables whenever investigations of cognitive ERPs are undertaken.