In Ecuador, reports of sexual assault have increased, and the investigation of these crimes is becoming increasingly important, as it provides key tools in a trial. The p30 is a marker that detects seminal fluid in cases of sexual assault, the sample is reliable 2 days, maximum 3 days after the act. Objective: To demonstrate that p30 positivity decreases according to the day of vaginal swab sampling in sexual crimes registered by the Flagrancia Quito unit. Methodology: An observational, analytical, cross-sectional study was conducted from the forensic reports of sexual crimes, sent to the DNA laboratory of the Prosecutor's Office, from January to July 2017.