BACKGROUND Primary lower-extremity hyperhidrosis (PLEH) can be treated by CT-guided lumbar sympathetic nerve modulation using absolute ethanol. However, doses of ethanol that are too high can cause nerve injury, and doses that are too low have suboptimal results. The present study aimed to investigate the dose-effect relationship of CT-guided lumbar sympathetic nerve modulation with absolute ethanol for PLEH. MATERIAL AND METHODS The study was conducted at the First Affiliated Hospital of Jiaxing University between 07/2014 and 02/2017. Twenty participants were enrolled in each group. The doses of absolute ethanol were 2.0 ml in the R₁ group, 2.5 ml in the R₂ group, 3.0 ml in the R₃ group, 3.5 ml in the R₄ group, and 4.0 ml in the R₅ group. Treatment effectiveness was assessed according to the time to complete hyperhidrosis relief: <10 min, effective; ≥10 min, non-effective. RESULTS The patient characteristics among the 5 groups were not statistically different (P>0.05). The onset time and time to complete hyperhidrosis relief decreased significantly with increasing dose of absolute ethanol (P<0.05). The effective rates in the 5 groups were 15.0%, 35.0%, 60.0%, 90.0%, and 100.0%, respectively. The ED₅₀ and ED₉₅ were 2.306 ml (95% CI: 2.003-2.512 ml) and 3.343 ml (95% CI: 3.051-3.962 ml), respectively. CONCLUSIONS This was the first dose-effect pilot study of consecutive PLEH patients treated by CT-guided lumbar sympathetic nerve modulation. CT-guided lumbar sympathetic nerve modulation with 2.306 ml (ED₅₀) and 3.343 ml (ED₉₅) of absolute ethanol showed treatment efficacy for PLEH. No complications were seen.