Infidelity in romantic relationships is a common occurence in modern relationships, especially in western cultures where it has been shown that it can be harmful for the relationship and wellbeing of both partners. Real or percieved threat to partner infidelity can result in negative outcomes such as partner violence (Whisman et al., 1997). Infidelity is a wide term that can come in a variety of different forms such as emotional, sexual, combined, and nowadays even online infidelity. Infidelity research often focus on how attitudes and intention of committing infidelity can affect actual behavior of infidelity. Besides that, other variables are also being associated with infidelity, some of them being personality facets, relationship satisfaction and sociodemographic variables like age, gender, religiosity and education level. The aim of this study was to investigate the role of attitudes, perceived behavioural control, subjective norms, relationship satisfaction and personality facets on the intention to commit infidelity in romantic relationships, and differences in attitudes towards infidelity, intention to commit infidelity and the actual behaviour of infidelity regarding gender, education level and religiosity of respondents. There were total of 359 respondents in this study (238 women, and 121 men). The age of respondents ranged from 18 to 74 years old (M = 32.98, SD = 12.69). The results have shown that attitudes towards infidelity, percieved behavioural control and subjective norms were all significant predictors of intention to commit infidelity in romantic relationships. Differences in attitudes towards infidelity, and intention to commit infidelity regarding gender, education level and religiosity were also examined where the results have shown that men have more positive attitudes towards infidelity and higher intention to involve in infidelity behaviours than women. Additionally, people with lower education level have had more positive attitudes towards infidelity and higher intention to commit infidelity behaviours than people with higher education level, but no differences were found in intention to commit infidelity regarding religiosity. No significant correlation between relationship satisfaction and intention to commit infidelity, or between relationship and intention to commit infidelity was found. The results of this study give evidence for the theory of planned behaviour regarding the specific behaviour of infidelity, gender differences that have consistently been shown in similar research, and the result that relationship satisfaction is in fact not in correlation with the intention to commit infidelity in romantic relationships. Contribution of personality facets in explaining intention to commit infidelity could not have been examined in this study, which supports inconsistency of research in this field.