Insomnia involves difficulty initiating, maintaining, receiving an adequate amount of, or returning to sleep. The study objective was to develop and validate a scale, the Catastrophic Thoughts About Insomnia Scale (CTIS), in order to assess the extent to which sleep-related catastrophic thinking contributes to the determination of sleep quality as assessed by psychometric questionnaires tapping self-reported insomnia severity. University student participants (N = 765) completed the CTIS as well as measures of sleep quality, insomnia severity, neuroticism, depression, and maladaptive thoughts about insomnia. Confirmatory factor and item response theory analyses were conducted for scale development. The proposed factor structure (i.e., rumination, magnification and helplessness subfactors with an overall catastrophizing factor) of an 18-item CTIS was supported. Validity was also supported. With further validation using clinical samples, the CTIS could reveal novel patient-specific treatment targets for insomnia patients and could serve as an assessment tool for the evaluation of therapeutic outcomes.