This cross-sectional study was carried out in order to determine the opinions of mothers on sexual development in children with intellectual disabilities. The sampling of this study included mothers of children aged 10-19 years with moderate and severe intellectual disabilities. Of the mothers, 45.7% stated that they felt incapable of providing sexual education to their adolescent children with disabilities and 97.6% stated that they had received no information on this subject themselves. Based on the mothers' opinions, the mean score for the sexual development of adolescent children was 11.33 ± 16.18. In the sub-dimensions of sexual arousal (20.97 ± 5.71), sexual harassment (12.22 ± 3.13), sexual satisfaction (15.79 ± 3.85) and sharing sexual issues (12.74 ± 2.67) the mean score of the scale was found to be high. The knowledge levels of the mothers concerning the sexual development of their children with intellectual disabilities were found to be low, and they required education on this issue.