A critical evaluation of the current available literature on Time Since Intercourse (TSI) was performed at the Centre of Forensic Sciences (CFS) to determine whether there is scientific support for reliable, evidence based opinions on TSI. The assessment included a review of published scientific literature and internal studies focusing on the persistence of spermatozoa, prostatic acid phosphatase and prostate specific antigen (PSA/p30) from internal samples of living individuals. From this review, it was concluded that, despite variation in sampling methodologies, there is scientific support for the development of TSI estimate guidelines based on the serological testing results from internal swabs and smears. (Published Abstract)