Insomnia catastrophizing has attracted attention in recent years. Individuals may have started to recognize the importance of evaluating the consequences of insomnia, which has worsened during the coronavirus disease 2019 (COVID-19) pandemic. Methods: The present study aimed to test the validity and reliability of the Insomnia Catastrophizing Scale (ICS) in the Turkish young adult population. The study group consisted of a total of 387 participants: 57 in the pilot study and 330 in the main study. The majority of the participants in the study were females. Results: According to the results of the confirmatory factor analysis, the single-factor structures of the ICS nighttime and daytime forms were confirmed to be the same as in the original structure, and the fit indices were above the acceptable limits. The ICS forms had very high reliability. Conclusions: The findings of the present study showed that the Turkish daytime and nighttime forms of the ICS are valid and reliable instruments. The results provide a means of measuring insomnia catastrophizing for use in therapeutic and counseling settings for Turkish young adult population. We also propose that mental health practitioners should design interventions to reduce insomnia catastrophizing in Turkish culture.