BACKGROUND: Skin antisepsis prior to the induction of spinal anesthesia is important because infectious complications may occur. Povidone-iodine and chlorhexidine have been widely used as antiseptic solutions for skin preparation; however, no study has been carried out to evaluate the efficacies of these antiseptic solutions for skin disinfection for spinal anesthesia. The aim of this study was to compare the efficacy of povidone-iodine and chlorhexidine by monitoring needle contamination rates during spinal anesthesia. METHODS: One hundred patients were randomly assigned to receive either 0.5% chlorhexidine in 70% isopropyl alcohol solution or 10% povidone-iodine aqueous solution for skin preparation. Patients' skin was disinfected three times in the lumbar area using the designated antiseptic solution and then allowed to dry for 3 minutes. After the induction of spinal anesthesia, the spinal needle and trocar were kept in a sterile culture bottle containing 45 ml of tryptic soy broth. The needles and trocars were then incubated under aerobic conditions for 48 hours at 37oC, and contaminated microbes were identified by routine microbiological methods. RESULTS: Five of the 51-povidone-iodine treated patient group showed positive culture growth, while no contamination was observed in 46 chlorhexidine treated patients. The microbial organisms found in the povidone-iodine group were Staphylococcus aureus, Escherichia coli, Acinetobacter lwoffii, Acinetobacter baumannii, and G (+) Bacillus species. CONCLUSIONS: 5% chlorhexidine in 70% isopropyl alcohol solution showed more potent anti-microbial effect than 10% povidone-iodine aqueous solution in terms of reducing the bacterial contamination rate of spinal needles.