Minoxidil is effective in inducing hair growth in patients with androgenetic alopecia by stimulating hair follicles to undergo transition from early to late anagen phase. However, there have been no controlled studies of topical minoxidil in Asian women. The objective of this trial was to investigate the efficacy of 1% topical minoxidil for androgenetic alopecia in Japanese female patients using a double-blind controlled method. This trial included 280 Japanese female patients aged 20 years or older with androgenetic alopecia who were administered either 1% topical minoxidil (n = 140) or placebo (n = 140) for 24 weeks. The primary efficacy variable was mean change from baseline in non-vellus hair count/cm(2). The mean change was 8.15 in the 1% topical minoxidil group and 2.03 in the placebo group, with a significant difference between groups (p < 0.001) [difference: 6.12 (two-sided 95% confidence interval (CI): 3.29-8.96)]. Secondary variables included investigators' assessments and patients' self-assessments. As assessed by investigators, 29.2% (40/137) of the patients had moderate or better improvement in the 1% topical minoxidil group compared to 11.8% (16/136) in the placebo group (p < 0.001 versus placebo). The effect on hair growth was assessed as improved or better by 36.5% (50/137) of the patients themselves in the 1% topical minoxidil group compared to 23.5% (32/136) in the placebo group (p = 0.019 versus placebo). The patients tolerated treatment with 1% topical minoxidil well without significant adverse effects.