Infidelity is a harmful and a main problem in the therapy of couple relationships. The present study examined the reliability, validity and factor structure of the attitudes toward the infidelity scale among the patients referred to counseling centers in Tehran. 528 participants (185 females and 343 males) were selected by convenience sampling method from 5 centers. The study instrument was Whately’s attitudes toward infidelity scale, which translated by 7 psychologists & back translated by an English expert. After a pilot study on 30 participants, the necessary corrections were made. The structure of the scale factor was confirmed in a first-order factor using confirmatory factor analysis. This scale had a good internal consistency (Cronbach's alpha=0.71 and test-retest=0.87) It had correlation with Alport internal and external religious orientation scale respectively 0.29 and 0.16, also negative correlation with Kansas Marital satisfaction scale and Enrich sexual satisfaction subscales (-0.22 and -0.16 respectively). This study showed that ATIS is an efficient tool for research and couple counseling and has an appropriate validity and reliability for Iranian society.