Purpose: To determine the internal consistency and 1-week test-retest reliability of the Problem Oriented Screening Instrument for Teenagers (POSIT) among adolescent medical patients.Methods: A research assistant administered the POSIT to a consecutive sample of 15- to 18-year-old patients arriving for routine medical care at a hospital-based adolescent medical practice. Each subject returned for a retest 1 week later. Internal consistency for each scale on test and retest was calculated using Cronbach alpha, and 1-week test-retest reliability by the intraclass correlation coefficient (r) and the kappa coefficient (κ).Results: The Substance Use/Abuse, Mental Health Status, Educational Status, and Aggressive Behavior/Delinquency scales had favorable alpha scores (> .70). Others, including Physical Health Status, had lower alpha scores. High intraclass correlation coefficients were found for all 10 POSIT scales (r = .72 to .88), although (r) was lower for males on two of the scales. Kappa coefficients for all scales indicated good reproducibility beyond chance (κ = .42 to .73).Conclusions: This study provided supportive evidence for the reliability of the POSIT in primary care medical settings, although some POSIT scales could likely be improved. The 20- to 30-min administration time is most practical in settings that are dedicated to adolescent medicine, and computerized administration and scoring are needed.