Background The 3D breast magnetic resonance fingerprinting (MRF) technique enables T1 and T2 mapping in breast tissues. Combined repeatability and reproducibility studies on breast T1 and T2 relaxometry are lacking. Purpose To assess test–retest and two‐visit repeatability and interscanner reproducibility of the 3D breast MRF technique in a single‐institution setting. Study Type Prospective. Subjects Eighteen women (median age 29 years, range, 22–33 years) underwent Visit 1 scans on scanner 1. Ten of these women underwent test–retest scan repositioning after a 10‐minute interval. Thirteen women had Visit 2 scans within 7–15 days in same menstrual cycle. The remaining five women had Visit 2 scans in the same menstrual phase in next menstrual cycle. Five women were also scanned on scanner 2 at both visits for interscanner reproducibility. Field Strength/Sequence Two 3T MR scanners with the 3D breast MRF technique. Assessment T1 and T2 MRF maps of both breasts. Statistical Tests Mean T1 and T2 values for normal fibroglandular tissues were quantified at all scans. For variability, between and within‐subjects coefficients of variation (bCV and wCV, respectively) were assessed. Repeatability was assessed with Bland–Altman analysis and coefficient of repeatability (CR). Reproducibility was assessed with interscanner coefficient of variation (CoV) and Wilcoxon signed‐rank test. Results The bCV at test–retest scans was 9–12% for T1, 7–17% for T2, wCV was <4% for T1, and <7% for T2. For two visits in same menstrual cycle, bCV was 10–15% for T1, 13–17% for T2, wCV was <7% for T1 and <5% for T2. For two visits in the same menstrual phase, bCV was 6–14% for T1, 15–18% for T2, wCV was <7% for T1, and <9% for T2. For test–retest scans, CR for T1 and T2 were 130 msec and 11 msec. For two visit scans, CR was <290 msec for T1 and 10–14 msec for T2. Interscanner CoV was 3.3–3.6% for T1 and 5.1–6.6% for T2, with no differences between interscanner measurements (P = 1.00 for T1, P = 0.344 for T2). Data Conclusion 3D breast MRF measurements are repeatable across scan timings and scanners and may be useful in clinical applications in breast imaging. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:1133–1143.