Orexin A and B are neuropeptides influencing, for example, arousal and respiration. Although panic disorder is characterized by both enhanced proneness for arousal and by respiratory abnormalities, the possible influence of orexin-related genes on the risk of developing this disorder has not been studied until now.We have analyzed the Ile408Val polymorphism in the hypocretin receptor 1 (HCRTR1) gene and the Val308Iso (G1246A) polymorphism in the hypocretin receptor 2 (HCRTR2) gene in a sample of 215 panic disorder patients and 454 controls.Although the polymorphism in the HCRTR1 did not differ between groups, the Iso allele of the HCRTR2 polymorphism was significantly more frequent in patients than in controls. After the population was divided according to sex, the association between the Iso allele of the Val308Iso polymorphism and panic disorder was observed only in female patients.Our results suggest that the HCRTR2 polymorphism may be of importance for the pathophysiology of panic disorder. The results should be regarded as preliminary until replicated in an independent sample. This indicates that further research on the possible role of orexin in panic disorder may prove rewarding.