Background: A growth factor cocktail (GFC) including fibroblast growth factor 9 (FGF9) in combination with microneedling is an effective and safe treatment for patients with androgenetic alopecia (AGA). However, there is a lack of studies evaluating its effects based on microneedle depth. Objective: This study aimed to evaluate the effects of a GFC including FGF9 on hair growth in patients with AGA, and compare the differences in efficacy according to microneedle depth. Methods: The study was performed on patients with AGA who were treated with topical GFC including FGF9 with microneedling once every 2 weeks for 3 months. The scalp was divided into right and left sides, and treated with GFC including FGF9 (right side) and normal saline (left side). The microneedle depth was 0.8 mm for both sides. A total of 22 patients (11 males and 11 females) were enrolled. GFC including FGF9 was topically applied with a microneedle medical device. Treatment efficacy was evaluated through phototrichogram and digital photograph analyses after 6 repeated treatments for 3 months. Results: The phototrichogram images showed that 3 months of treatment with GFC including FGF9 with microneedling increased hair density (27.4±4.4/cm2) and diameter (2.7±2.7 μm); increases in hair density (5.7±4.4/cm2) and diameter (2.2±2.3 μm) were also seen in the region of the scalp that received normal saline. These results were statistically significant (p＜0.05). The treatment effect was not significantly different between microneedle depths of 0.8 mm (used in this study) and 0.5 mm (used in our previous study) in terms of both hair density and hair diameter. Conclusion: GFC including FGF9 with microneedling is an effective and safe treatment for patients with AGA. According to the results of this study and our previous report, we believe that microneedle depths of 0.5∼0.8 mm can sufficiently stimulate the scalp to increase drug-delivery. (Korean J Dermatol 2017;55(8):504∼510)