BACKGROUND: We prospectively examined the influence of young women's depression and stress symptoms on their weekly consistency of contraceptive method use. STUDY DESIGN: Women ages 18-20 years (n = 689) participating in a longitudinal cohort study completed weekly journals assessing reproductive, relationship and health characteristics. We used data through 12 months of follow-up (n = 8877 journals) to examine relationships between baseline depression (CES-D) and stress (PSS-10) symptoms and consistency of contraceptive methods use with sexual activity each week. We analyzed data with random effects multivarible logistic regression. RESULTS: Consistent contraceptive use (72% of weeks) was 10-15 percentage points lower among women with moderate/severe baseline depression and stress symptoms than those without symptoms (p < .001). Controlling for covariates, women with depression and stress symptoms had 47% and 69% reduced odds of contraceptive consistency each week than those without symptoms, respectively (OR 0.53, CI 0.31-0.91 and OR 0.31, CI 0.18-0.52). Stress predicted inconsistent use of oral contraceptives (OR 0.27, CI 0.12-0.58), condoms (OR 0.40, CI 0.23-0.69) and withdrawal (OR 0.12, CI 0.03-0.50). CONCLUSION: Women with depression and stress symptoms appear to be at increased risk for user-related contraceptive failures, especially for the most commonly used methods. IMPLICATIONS: Our study has shown that young women with elevated depression and stress symptoms appear to be at risk for inconsistent contraceptive use patterns, especially for the most common methods that require greater user effort and diligence. Based upon these findings, clinicians should consider women's psychological and emotional status when helping patients with contraceptive decision-making and management. User-dependent contraceptive method efficacy is important to address in education and counseling sessions, and women with stress or depression may be ideal candidates for long-acting reversible methods, which offer highly effective options with less user-related burden. Ongoing research will provide a greater understanding of how young women's dynamic mental health symptoms impact family planning behaviors and outcomes over time.