Among the many factors that affect the degree of completion and satisfaction of breast reconstruction, the scarring is one issue that a surgeon cannot completely control. We hypothesized that the administration of cytotoxic drugs following the immediate breast reconstruction using transverse rectus abdominis musculocutaneous (TRAM) flap might affect the process of scarring, thus resulting in reduced incidence of hypertrophic scarring at the donor site. Data have been collected from 1,000 consecutive patients between July 2001 and December 2009. The relationship between the adjuvant chemotherapy and the incidence of hypertrophic scarring was studied, and the influence of other presumed risk factors was analyzed. The incidence of hypertrophic scarring was 18.6 % (75 of 404) in the non-CTX group and 3.8 % (20 of 530) in the CTX group. Univariate analysis using logistic regression modeling confirmed the statistical significance of the reducing effect of chemotherapy on the incidence of hypertrophic scarring (p < 0.001; OR: 0.172). The incidence of donor-site hypertrophic scarring following immediate TRAM breast reconstruction was found in nearly 20 % of the patients without chemotherapy, showing a significant difference from the patients with chemotherapy. We believe that Asian patients who undergo immediate TRAM breast reconstruction without chemotherapy are a high-risk group that is prone to hypertrophic scarring, requiring active preventive measures.