A new method for the rapid assessment of neonatal withdrawal was tested. Three studies with 80 newborns compared the reliability, sensitivity and specificity of the Neonatal Withdrawal Inventory (NWI) with that of the Neonatal Abstinence Scoring System (NASS), a widely used neonatal withdrawal scale. Interrater reliability for raters assessing neonatal withdrawal with the NWI (range, 0.89-0.98) was superior to that demonstrated by the same raters using the NASS (range, 0.70-0.88). With the NASS as the standard, the sensitivity and specificity of the NWI were 100% at syndrome detection and treatment threshold levels. With use of the NWI, the severity of neonatal withdrawal could be accurately assessed in 10 minutes under case-blinded conditions. The NWI's advantages include brevity, ease of administration, and flexibility. The NWI's simplicity and accuracy commend its wider use as a clinical and experimental tool.