Measurement Invariance of the Brief State Rumination Inventory Across Administration Methods, National Samples, and Sex

State rumination is a temporary activation of repetitive, negative, self-focused thinking in response to specific situational triggers or mood states. We present the results of two studies that examined the psychometric properties and measurement invariance of the Italian version of the Brief State Rumination Inventory (BSRI). Study 1 tested its unidimensionality and measurement invariance across administration methods (paper-and-pencil, N = 216, vs. online, N = 222) and national samples. Study 2 (N = 675) tested its measurement invariance across sex and its construct validity. Results supported the BSRI’s unidimensional structure. Configural and weak (metric) invariance were supported across administration methods and national samples, whereas partial strong invariance was established across sex. The Italian BSRI showed construct-validity evidence consistent with theoretical expectations, correlating more strongly with brooding than reflection and more strongly with depression than anxiety or stress. Neuroticism and limited access to emotion regulation strategies emerged as other significant correlates. These findings support the Italian BSRI as a robust tool for assessing state rumination.