Child sexual abuse myths legitimize abusive behaviors, involving high levels of victim blame and low levels of offender liability. The present study aims to: (i) adapt a measure of endorsement of child sexual abuse myths to the Portuguese context (i.e., Child Sexual Abuse Myth Scale–CSAMS); and (ii) provide validity and reliability evidence for this measure. A total of 423 adults (66.2% female) filled out a sociodemographic questionnaire, the Ambivalent Sexism Inventory, and the CSAMS. The CSAMS validity and reliability results supported the original structure, which comprises three dimensions: Blame Diffusion (e.g., ‘Adolescent girls who wear very revealing clothing are asking to be sexually abused’), Restrictive Stereotypes (e.g., ‘Most children are sexually abused by strangers or by men who are not well known to the child’), and Denial of Abusiveness (e.g., ‘Older children, who have a better understanding of sexual matters, have a responsibility to actively resist sexual advances by adults’). Configural and metric invariance by sex were held, and criterion validity was observed through significant associations between myths, sexism and sex. This study provided evidence in support of the validity and reliability of the Portuguese version of the Child Sexual Abuse Myth Scale.