<h3>Background/introduction</h3> Testing for STI’s following sexual assault is routine. In cases were there is no other sexual activity other than the sexual assault, the assailant may be the source, and a positive result of significance in criminal investigation. <h3>Aim(s)/objectives</h3> The potential forensic significance of STI results should be considered in each case. <h3>Methods</h3> Discussion on information sharing of STI results is undertaken in cases referred to a sexual assault referral centre (SARC) with an absence of other sexual activity. This is documented and includes interpretation of results. <b>Case 1: </b>An adolescent female, not previous sexually activity, vaginally raped, had a bacterial STI screen and serum save taken hours after the assault. Genital discomfort subsequently developed. A presumptive diagnosis of genital herpes made and tested. Herpes antibody testing was requested on samples taken; initially, when symptomatic and post symptoms. <b>Case 2: </b>An elderly female, widowed several years earlier and sexually inactive since was vaginally raped. A bacterial STI screen was taken at the time initially and 14 days later. <h3>Results</h3> <b>Case 1 – </b>HSV Type 2 confirmed. HSV antibodies initially absent were demonstrated in the post symptomatic sample. <b>Case 2 – </b>Initial <i>Chlamydia trachomatis</i> NAAT tested negative with a positive result at 2 weeks. <h3>Discussion/conclusion</h3> The results are supportive of the assailants as the source. The positive Chlamydia result supported the penile vaginal penetration described, allowing consideration of a rape charge rather than a lesser offence. In both cases admissions were made pre-trial avoiding victims being called to court.