Worry is a popular phenomenon and a common feature of many disorders, especially anxiety disorders. The objective of the study was to predict worry by using three predictive factors related to biological, emotional and cognition areas. In this study, behavioral inhibition, behavioral activation system, difficulties in emotion regulation and metacognition were examined as predictive variables. In a correlation cross-sectional design, 234 Medical Group students [BA and MA] of Tehran University of Medical Sciences participated in this study by using cluster sampling. The students completed these scales: Behavioral Inhibition and Behavioral Activation Systems (BAS/BIS), Difficulty of Emotion Regulation Scale (DERS), Metacognition Questionnaire-30 (MCQ-30) and Penn State Worry Questionnaire (PSWQ).Behavioral inhibition system, difficulty of emotion regulation and metacognition variables were significantly positively correlated with worry (P<0.01). Behavioral activation system variable was not significantly associated with worry. Stepwise multiple regression analysis indicated a predictive model for worry in which behavioral inhibition system, difficulty of emotional regulation and metacognition were its components respectively. Behavioral activation system was not included in the model. The findings of this study that worry should be studied in different biological, emotional, and metacognitive aspects. The results also emphasize the role of behavioral inhibition system as a temperamental and biological factor in psychopathology of worry in adult population.