Introduction Extended transrectal ultrasound-guided prostate biopsy is a state-of-the-art tool for prostate cancer detection. Nevertheless, approximately 1/3 of cancers are missed when using this method and repeat biopsy sessions are often required. The aim of this study was to investigate how sampling density (a compound variable reflecting the number of biopsy cores and prostate volume) impacts on detection rate in multiple repeat TRUS-biopsies. Material and methods A total of 1007 consecutive patients undergoing their 1st, 2nd, 3rd and any further repeat prostate biopsies were included. The relationship between sampling density and other clinical variables (age, prostate-specific antigen level, free/total PSA ratio, digital rectal examination, number of previous biopsies) and cancer detection rate were assessed by interaction analysis. Results There were 562 primary re-biopsies, 267 second re-biopsies and 178 third and further re-biopsies included in the study. Detection rate was 25.4%, 25.8% and 25.3%, respectively. Interaction of sampling density with age was demonstrated in patients undergoing their first repeat biopsy (but not further rebiopsies). No interaction was observed with other variables investigated. Conclusions A more extensive prostate sampling leads to a higher cancer detection rate on repeat prostate biopsies, as shown previously. However, this effect seems to be particularly pronounced in men younger than 65 years undergoing their first repeat prostate biopsy.