Objective: To assess whether worry and rumination differ in predicting nighttime sleep disturbance versus daytime sleep-related impairment, as assessed using short forms from the Patient Reported Outcomes Measurement Information System (PROMIS). Participants: Adults recruited from the United States population (N = 459) via an online crowdsourcing service. Methods: Factor analysis explored whether items comprising validated measures of worry and rumination loaded onto separate factors. Hierarchical multiple regression models entered worry and rumination in a stepwise fashion to assess their relative strength in predicting PROMIS sleep disturbance and sleep-related impairment, after controlling for 17 covariates. All analyses were run twice using sleep-specific and general measures of worry and rumination. Results: Worry and rumination items loaded onto separate factors. In the regression analysis of sleep-specific cognition, only worry entered the model predicting sleep disturbance, whereas rumination entered after worry in the model predicting sleep-related impairment. In the analysis of general cognition, both cognitive process variables significantly predicted the PROMIS outcomes. Worry was the stronger predictor of sleep disturbance, whereas rumination was the stronger predictor of sleep-related impairment. Conclusions: Worry and rumination were observed to be distinct constructs that separately contributed to predicting daytime sleep-related impairment. Future studies should more closely examine how cognitive processes relate to insomnia symptomology during the day.