Background Sexual fantasies represent a cognitive pattern that influences sexual activation and desire. This study aims to investigate the relationship between sexual fantasies, sexual desire and overall sexual functioning among Iranian adults.Methods A total of 1353 volunteers from the general population participated by filling out questionnaires including, the Sexual Desire and Erotic Fantasies Questionnaire, the International Index of Erectile Function and the Female Sexual Function Index. Sexual fantasies were categorized based on predefined criteria. Statistical analyses were conducted using correlation and regression techniques to explore these relationships.Results Men reported more explicit sexual fantasies, including active roles, common sexual behaviours and dominance, during sexual activities (mean 1.62, s.d.1.16), taboo elements (e.g. sex with minors, animals, family members and rape; mean 0.38, s.d. 0.60) and fantasies with diverse partners (mean 5.18, s.d. 4.16). In contrast, women preferred romantic content (mean 1.97, s.d. 0.97) and a passive role. No gender differences were observed in bondage, dominance, sadism and masochism fantasies. Both genders showed a strong correlation between sexual fantasies and sexual desire (Men 0.461, Women 0.372).Conclusion Understanding these patterns in a conservative country, such as Iran, may contribute to culturally sensitive intervention in traditional culture. For instance, in sex therapy or workshops for couples on utilizing fantasy to enhance sexual satisfaction, subject to the values of modesty and privacy. This research reveals valuable insight into sexual imagery and sexual performance, and fills a gap in cultural studies. However, further research is needed to validate these findings.