The aim of this descriptive study was to investigate the impact of body image, insight, and mental health confidence on medication adherence among young adult women with mental disorders. Data collection occurred from August to September 2018. The study participants were 147 young adult women aged 19 to 45 with mental disorders who were psychiatry outpatients either getting treatment in general hospitals located in Seoul and Gyeonggi Province or receiving rehabilitation therapy through local mental health welfare centers in Korea, and agreed to participate in the study. The measurement tools used were the Body Image Scale; the Scale to Assess Unawareness of Mental Disorder, Korean short-form version; the Korean version of the Mental Health Confidence Scale; and the Korean version of the Medication Compliance Scale. The collected data were analyzed using descriptive statistics, t-test, analysis of variance, Pearson correlation analysis, and multiple regression analysis in SPSS/WIN 25.0 (IBM Corp., Armonk, NY, USA). Medication adherence among the study participants differed by age (F = 2.95, p = 0.042), religion (t = −2.06, p = 0.042), level of trust in psychiatrists (F = 5.40, p = 0.006), treatment duration (F = 4.48, p = 0.005), and noncompliance to medication regimens due to weight gain (t = −2.61, p = 0.010). Multiple regression analysis demonstrated that body image (β = −0.32, p < 0.001), insight (β = −0.24, p = 0.002), and mental health confidence (β = 0.24, p = 0.004) had a significant impact on the medication adherence of the participants. Body image, in particular, had the greatest influence on the medication adherence of the participants. This study found that body image, insight, and mental health confidence were important in improving medication adherence among young adult women with mental disorders. Practical, patient-centered, and individualized approaches that can improve medication adherence by seeking to understand negative perceptions regarding body image should be considered.