In the quest to uncover lower order processes that underlie anxiety disorders, researchers have proposed a number of fundamental fears, which are thought to represent fears of inherently aversive stimuli that can explain a number of higher order constructs such as more specific fears. In a recent theoretical article, Carleton narrowed the list of potential fundamental fears down to three candidates: fear of death, fear of pain, and fear of the unknown. Carleton proposes that fear of the unknown represents the primary fundamental fear, suggesting that unlike the other two, fear of the unknown is inherently aversive and logically irreducible. The present study represents an initial empirical investigation of this hypothesis. In a cross-sectional study (N = 373), fear of death, fear of pain, and fear of the unknown were assessed as simultaneous predictors of anxiety. Results showed that fear of the unknown was indeed the strongest unique predictor, while fear of pain also uniquely predicted anxiety, although to a lesser extent. While the results suggest that fear of the unknown may indeed be the most fundamental fear, the need for conceptual clarification and empirical work using diverse measures is discussed.