An original Rumination Questionnaire (RQ) is presented. This is a 20-item two-factor questionnaire measuring the frequency of experiencing negative, unwanted, recurring thoughts about self or the social world. Studies on 13 samples showed two-factorial structure of RQ as well as high internal consistency and test-retest reliability of the two scales constituting the RQ: The scale of rumination about self and the scale of rumination about the social world. Both kinds of rumination correlated with various indices of anxiety, depression, and decreased mood. Rumination about self correlated with decreased self-esteem and satisfaction with personal domains of life. Rumination about the social world correlated with decreased satisfaction with public areas of life. A study of a representative sample of Polish adults showed a much higher tendency to ruminate about the social world than about self. Rumination about world increased, while rumination about self decreased with age.