Gentamicin, whether administered either intravenously, incorporated into bone cement or for local intra-operative irrigation, is a commonly used antibiotic in orthopaedic practice. The former two have been well studied, however the literature on the therapeutic efficacy and safety of gentamicin irrigation is sparse. The objective of this study was to assess systemic absorption of gentamicin irrigation in joint replacement surgery. This was a non-randomised, prospective study. Ninety-eight patients (group A) who underwent total joint replacement and 40 patients (group B) who underwent hemi-arthroplasty were treated intraoperatively with gentamicin irrigation. Serum gentamicin levels were assayed at 4 hours and 24 hours post-surgery. Sixteen of 98 patients in group A (16%) and 12 out of 40 patients in group B (30%) were found to have serum gentamicin level above 2mcg/ml at 4 hours post-surgery. We conclude that intra-articular gentamicin irrigation is systemically absorbed at substantial levels.