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Objectives: Hoarding disorder is a complex condition that significantly impacts individuals' lives, characterized by excessive acquiring, difficulty discarding, clutter, distress, and impairment. This study aimed to examine the extent to which genetics and environment influence difficulty discarding, excessive acquisition, and clutter through the implementation of a classical twin study. Methods: A total of 194 twins, consisting of 100 monozygotic (MZ) and 94 dizygotic (DZ) twins, participated in this study. Hoarding symptoms was assessed using the saving inventory-revised.  To estimate the heritability of hoarding symptoms, the classical univariate twin model was employed. Results: Based on the univariate analysis, it was found that the heritability estimates for difficulty discarding and excessive acquisition are 0.43 and 0.52, respectively. However, the results did not provide support for the role of genetics in clutter. Instead, it was indicated that the common environment accounts for 0.54 of the variance in clutter, while the specific environment contributes 0.46 to this symptom. Conclusion: The difficulty discarding and excessive acquisition have been found to be moderately heritable. On the other hand, considering the contribution of genetics and environment to clutter, the results raise doubts about the association of clutter with hoarding. The relatively low genetic influence suggests that this trait may overlap with other behaviors rather than hoarding.