Background and aims: Sexual addiction is a pathological behavior characterized by a combination of excessive
sexual desire and impaired ability to control it. Its incidence ranges between 1.2% and 32.2%, although this number
may vary depending on the screening tool used. This wide variability is largely due to the use of non-validated
instruments (e.g., structural validity relying on exploratory analyses, instruments translated without an additional
validation process, or instruments validated in another format). To deal with these limitations, this study tested the
psychometric properties of the Spanish paper-and-pencil and online versions of the Sexual Addiction Screening Test
(SAST). Methods: A total of 2,528 participants (1,163 males) completed the Spanish version of the SAST, along with
other instruments assessing sexual compulsivity (1,585 = paper-and-pencil, 943 = online). Results: The exploratory
factor analysis yielded a four-factor structure explaining 57.39% of the variance for the SAST paper-and-pencil
version. This factor structure was then verified for the online version through the use of confirmatory factor analysis
[χ2(264) = 441.59; χ2/df = 1.66; RMSEA = 0.02; CFI = 0.94; IFI = 0.94]. This methodology was also used to support
measurement invariance (configural, metric, and scalar invariance) according to gender. The reliability of the total
score ranged from .82 to .85. Similarly, correlations with related scales were positive and significant (r between .22
and .71). Temporal stability 1 year after the first application was 0.65 (paper-and-pencil format) and 0.60 (online
version). Conclusion: These results, together with the absence of questionnaires translated into Spanish to assess this
construct, justify the use of the SAST in the evaluation of sexual addiction in Spanish-speaking countries.