Background and aims The Internet is widely used for sexual activities and pornography. Little is known, however, about why people look for meetings and sexual interactions through the Internet and about the correlates of cybersex addiction. The goal of this study was to construct a questionnaire for cybersex motives [Cybersex Motives Questionnaire (CysexMQ)] by adapting the Gambling Motives Questionnaire to cybersex use and validating its structure. Methods Two online samples of 191 and 204 cybersex users were collected to conduct a principal component analysis (PCA) on the first sample and a confirmatory factor analysis (CFA) on the second. Cronbach's α and composite reliability were computed to assess internal consistency. Correlations between the CysexMQ and the Sexual Desire Inventory (SDI) were also evaluated. Results Two competing models were retained from the PCA, one with two factors and the other with three factors. The CFA showed better fit for the three-factor solution. After three cross-loading items were removed, the results showed that a final 14-item three-factor solution (enhancement, coping, and social motives) was valid (adjusted goodness-of-fit index: 0.993; normed-fit index: 0.978; Tucker–Lewis index: 0.985; comparative fit index: 0.988; root mean square error of approximation: 0.076). Positive correlations were found between the different motives and the subscales of the SDI. Discussion The results suggest that the CysexMQ is adequate for the assessment of cybersex motives.