Background: Few victims of sexual assault (SA) report to the police. Belgian Sexual Assault Care Centres (SACCs) offer holistic care to victims of SA, including the possibility to report to the police on site. This study aims to identify the association of victim-, assailant, victimisation-incident and support characteristics with reporting rates among SA victims attending the Belgian SACCs. Methods: Data on SACC victims were routinely collected in electronic patient files between 25 October 2017 and 31 October 2019. Both unadjusted and adjusted binary logistic regression models were fitted to assess the relation between the above-mentioned characteristics and reporting rates. Results: The majority of 931 victims (68.7%) reported to the police. Victims who experienced physical SA without penetration were more likely to report than rape victims (aOR 1.98, p=0.015); those with an unknown type of SA were less likely to report (aOR 0.27; p<0.001). Compared to victims who presented to the SACC within 72 hours after the SA, those presenting later than one week or for who the delay was unknown were less likely to report (1 week – 1 month: aOR 0.35; p<0.001; > 1 month: aOR 0.21; p<0.001; unknown: aOR 0.17; p<0.001). Victims accompanied by a confidant at the SACC had higher odds to report than those presenting alone (aOR 1.68; p=0.004). SACC site was significantly associated with reporting to the police (aOR 1.92; p=0.002; aOR 1.89; p=0.003). Conclusion: This study reveals the importance of victims’ support persons in reporting SA to the police, what so far has received little attention in quantitative research. Interventions targeting support persons may be key to alter reporting behaviour among victims of SA. Reporting SA to the police can however not be seen independently from the overall help-seeking behaviour of victims and should as such be part of holistic care to victims of SA.