Prevention as intervention is identified as a middle-range theory consistent with the Neuman systems model. Through an examination of anxiety research using Neuman's theory, prevention as intervention is examined for clarity, simplicity, generality, accessibility and importance. Conceptual clarity is in need of improvement to proceed with theory testing research. Until such concepts as the flexible and normal lines of defence, created environment, and the inter-relatedness of core system variables are further understood, the theory of prevention as intervention remains unclear.