Adolescence is associated with an increase in the rate of certain psychiatric symptoms, and itis typically the developmental period when prodromal features of the major psychiatric disordersemerge. This is especially true of schizophrenia, with the majority of patients showing a markedpostpubertal rise in schizotypal signs that predates the onset of clinical symptoms in earlyadulthood. Cross-sectional studies of youth have revealed a positive correlation between age andsaliva cortisol level, suggesting a normative maturational increase in activity of thehypothalamic–pituitary–adrenal (HPA) axis. It has been hypothesized that thisincrease may trigger the expression of symptoms in vulnerable individuals. The presentlongitudinal study measured cortisol secretion and its relation with symptom development insamples of youth with schizotypal personality disorder (SPD), other personality disorders, or noAxis II disorder. The findings indicate moderate stability in cortisol levels across a 2-year period,with a longitudinal increase in cortisol levels over time. Cortisol levels at the first and secondassessments were correlated with the severity of SPD symptoms at follow-up. The results areconsistent with the notion that the HPA axis undergoes a postpubertal maturational process thatmoderates the expression of psychiatric symptoms.