Adolescent pain is common and continues into adulthood, leading to negative long-term outcomes including substance-related morbidity: an empirical definition of its construct may inform the early detection of persistent pain trajectories. These secondary analyses of a classical twin study assessed whether: headaches, back pains, abdominal pain, chest pains, stabbing/throbbing pain, gastric pain/nausea, measured in 501 pairs across 5 waves between age 12-17, fit a unitary construct, or constitute independent manifestations. We then assessed which symptoms were associated with a steady, 'frequent pain' trajectory that is associated with risk for early opioid prescriptions. Item Response Theory results indicated that all 6 pain symptoms index a unitary construct. Binary logistic regressions identified 'back pain' as the only symptom consistently associated with membership in the 'frequent adolescent pain' trajectory (OR:1.66-3.38) at all 5 measurement waves. Receiver Operating Characteristic analyses computed the discriminating power of symptoms to determine participants' membership into the 'frequent' trajectory: they yielded acceptable (.7-.8) to excellent (.8-.9) area under the curve (AUC) values for all 6 symptoms. The highest AUC was attained by 'back pain' at age 14 (.835); for multiple cut-off thresholds of symptom frequency, 'back pain' showed good sensitivity/false alarm probability trade-offs, predominantly in the 13-14-15 age range, to predict the 'frequent pain' trajectory. These data support a unitary conceptualization and assessment of adolescent pain, which is advantageous for epidemiological, clinical, and translational purposes. Persistent back pain constitutes a sensitive indicator of a steady trajectory of adolescent pain.