Introduction: In recent years, greater attention has been paid to research on sexual satisfaction because of its association with general well-being and increased interest in sexual and public health issues. Objectives: The objective of this study was to evaluate the psychometric properties of the Satisfaction with Sex Life Scale (SWSLS). Methods: 2,154 Portuguese individuals (M = 34.67 years, SD = 17.18) participated. Confirmatory factor analysis (CFA) and item response theory (IRT) were used. Specifically, the internal structure, reliability and factor invariance of the SWSLS were evaluated by sex and age, as well as the characteristics and performance of the items based on the IRT analysis. Results: The SWSLS Confirmatory Factor Analysis confirmed that a one-dimensional model fit the data well, both for the total sample and for each sex and age group. Furthermore, the SWSLS has adequate reliability for internal consistency. Factor invariance across sex and age was supported by confirmatory multigroup factor analysis. The graduated response model showed a good fit for the one-dimensional model, while the item and test information curves indicated that the SWSLS is more informative to identify high levels of sexual satisfaction. Conclusion: The SWSLS has adequate psychometric properties to measure general sexual satisfaction in the Portuguese population regardless of age and sex.